I actually don't see it as all that odd that someone might want to use grooves from BFD (or any other drum sampler) and apply them to AD2 (or any other sampler... like BFD).
Thing is sometimes a specific kit or sound in one sampler is just better for the material. I have an Andy John's kit that's locked to SD3 I intend to use actually even though SD3 is of course inferior to BFD and AD2 (but still not a total dog... it works fine for simple playback and edits).
I've actually put a lot of thought into this stuff and even had to do a conversion recently from an EZD program to AD2 (because I don't own EZD and I wanted to use my AD2 Metal Kit... but I may have wanted to use BFD Eco which I also own).
Anyway... what I discovered is using the onboard conversion maps in these programs (like the ones that will supposedly take a MIDI part created in one program and translate them to the MIDI map in another program) don't work all that great. They kind of do but there's always some wierd mismatch that has to be dealt with. Still that's one option and even if there isn't a direct conversion map I found you can get pretty close just messing around with the various HARDWARE maps these programs have that take the default MIDI messages from things like V-Drums or other MIDI kits. Just cycle through the maps and see what syncs up best then you can just manually alter any wonky MIDI notes.
The other similar option is to create drum maps that will do the conversion. I haven't tried this yet but from my studies this is an option... but a laborious one.
Honestly though the thing that I found provided the BEST results was simply editing the specific notes en masse in the PRV to match the default AD2 MIDI map (and this of course would apply to any sampler).
In my case I was using an entire song that had been programmed using EZD so really I only had one clip to deal with and it was pre programmed which avoids issues you may run into (but I will attempt to show how to apply this to other scenarios after I describe the basic procedure).
What I did was the following...
1) Imported the entire EZD created MIDI clip into the project. Of course it did not match up to the AD2 map so it needed to be corrected.
2) I opened the clip in the PRV and set my zoom level so I could see all the various hits in the project vertically (and at first horizontally as well to make sure I was viewing ALL the hits including weird one off hits). I was lucky because I had an audio file reference to guide me but it's usually pretty obvious what's a kick and sanre and hat, etc. Otherwise I would have needed the actual synth to play it back for reference (which in this case I did not) but I will describe that later).
3) Of course I will have inserted AD2 (or for general purposes we can call it the "target sampler") and made the necessary routing to trigger it from the MIDI track/clip. I used the AD2 interface (or target sampler) to choose my kit pieces or a kit preset and got a general idea of which MIDI notes would trigger the most important kit pieces (kick, snare, hats, ride which is really only four kit pieces and their articulations are usually within a chromtic MIDI note or two from the main artics).
4) In the PRV the goal is simply to drag those main kit piece hits to the correct notes so they trigger the target sampler. So if I know that AD2's default kick is at C1 (for example... can't remember if that's the actual default) I simply drag all the notes in the MIDI track that I know to be the kick hits to C1 in the PRV. The procedure to do this efficiently is...
4a) Click on the piano key in the PRV where all the Kick hits from the source sampler are (so in my case let's say the MIDI note for the kick from EZD were at D1... which they aren't but whatever). Doing that selects ALL the MIDI notes in that row. Essentially you have just selected ALL the kick hits in the clip (or at least that articulation of the kick).
4b) Using the Smart Tool or Move tool just hold the Shift Key (which contrains movement to one direction so dragging up they will stay in time), left click then drag those notes up to the proper note to trigger the kick in AD2 (so in my hypothetical that would be C1). If you are using the correct tool in the correct way (be sure to hold shift) then just that row of notes will move without any additional screwing around. Test it out by starting playback after the move but as you move the notes you'll hear what kit piece each PRV key/note triggers what in the target synth so you can really just listen as you drag until you hear the Kick sound then drop the notes.
5) Repeat this for all the main kit peices in the clip/track. After the kick you'll probably want to do the main snare hits which may have two articulations then a bunch of one off articulations then maybe weird stuff like stick hits/rimshots. So just be aware of what's one and drag to the right place... mostly though you're gonna want to focus on the snare hits crucial to the main beat at first and correct the rest later. Then the hi hat and/or ride.
6) Listen back to make sure you have the main beat down and your kick, snare, hats, ride are all triggering the right kitpiece in the target sampler.
7) As you listen back obviously the missing tom fills, cymbal crashes, perc slot stuff and whatever other weirdness is going to stand out. So you basically just do exactly the same process as before except for all the fancy accent stuff. It will be much easier to figure out what goes where because you have your main beat chugging along to compare it to. As I said I had a reference track with the original drum part so it was easy to figure out what those extra weirdo notes were and just needed to drag them to the appropriate slot. Without some kind of reference that of course would be harder.
So now what to do if you are working with a reference track or a single written track (like if you were still writing your sang and wanted to use the MIDI files provided with various samplers and then put through one sampler)...
I would set up all the samplers in the project. So if you wanted to use BFD MIDI grooves in AD2 and build your song that way... well if you ONLY wanted to use BFD grooves and then send them to AD2 just build up your drum track in a BFD track, copy it to the AD2 track and do what I descibed above. That's easy enough... you don't need your final drum sound in place, you just need to hear the beat on a semi similar kit to the one you intend to use.
However if you want to use a MIXTURE of one or more sampler MIDI groove libraries (which I do intend to in the future) then you drag the MIDI Groove clips from the various sampler libraries into the corresponding track that you have set up in the project for that library and build you beat/drum track that way.
So... set up an AD2 track and a BFD track (or if you have other samplers with their own libraries you want to raid like SD3 or EZD or whatever). They should all be audible and playing back whatever you throw into their source MIDI tracks. Probably best to use Simple Instrument Tracks for all of this until you have the parts written, mapped and ready to go... THEN turn it all into a multi out setup after you are confident the song is written/structured.
If you find a groove/fill you like in the BFD library drag it into the BFD MIDI source track at the correct point in time. If you find a groove/fill you like in the AD2 library drag it into the AD2 MIDI source track to the correct point in time.
etc...
It will sound weird having multiple kits playing back (so try to match kit presets so it's not too drastic of a difference) but at least you can hear the fills and beats which is enough to build up the song structure.
Once you have the song structured then you need to simply make it so the BFD clips trigger AD2. I'd like to say that you can just Bounce to Clips and then copy the BFD clip into a new take lane in the AD2 track but that actually does some screwy stuff. I think a better option is to simply reroute the BFD Track to the AD2 sampler (you just have to change the output of the BFD MIDI Source track to AD2 and it should work). Bounce to clip those BFD clips so it's one long clip, open it in PRV and click/drag the notes where they need to be to trigger AD2 properly.
If you are using multiple groove libraries from multiple samplers then of course you have to do that for each track.
Once you are done remapping all your clips from all the various samplers copy/paste all those clips into new take lanes of the target sampler's track. Mute the other tracks and play it back to make sure it worked. If it did then select all the clips you just moved into the target sampler's track (including any other clips in that track), do a Bounce to Clips so everything turns into one full clip and there you have it. A bunch of drum groove clips yanked from multiple sources all playing through whatever synth you want.
NOTICE: I did not proofread this post and this is merely a hypothetical procedure I have not FULLY tested but I have tried out a few things that indicate this type of thing would work. Obviously a rather laborious process but in other ways it might make some otherwise impossible creativity options possible. I for one do not like being restricted to a single library.
It is also the type of thing that the drum sampler companies should be working together on solving. They need to cooperate and standardize their maps.
Cheers.