HELP: Roland TD12 to My Roland Octacapture to My Computer for MIDI Triggers

Yes that will work fine, not sure why you want it to go through the octacapture?  I would try both
ways , there should be not difference in midi timing but it would be good to test both ways out.
   but the answer to your question is yes it will work :)

Thanks for the advice on this and yea I will definitely use AD2 with it via MIDI.  I really appreciate it and I will be testing it today. I will confirm afterwards that I got it working, or if I have any issues. I can't wait to get it setup. 

As long as the audio interface is fast enough there's no need to listen to the audio output of the TD-12 brain. 
 
There are plenty of tips to reduce latency in the Sonar section of the forum.  A few highlights being 1) to ensure you do not have any network adapter active (or wireless adapter) while recording/tracking and 2) to not have effects active on any tracks while recording.
 
However, that said, if the audio interface is not that snappy, then the converse strategy is to listen only to the TD-12 audio output (for the drums mixed in with the other playback tracks of the song), and not listen at all to AD2.  That also is a reliable strategy.  Then after recording the drums, you go back and listen to what you performed through AD2, and have the TD-12 output complete off.  The disadvantage of that is you can't take advantage of what you might have set up in AD2 to hear while playing/performing the drums.  The advantage is that you can be spot on with timing.
 
But, if you have next to no latency, as outlined at the start, it's better to only monitor through AD2 and have the TD-12 audio output completely silent while tracking/recording.

Cactus Music
Yes absolutely system dependent. He has a Roland interface which I do believe are not great performers. 

Very true. I could never play AD2 or Kontakt drums via my TD20 when still using Roland interfaces. The lowest buffer setting would still yield a minor latency that felt odd and unnatural.

You need a top notch RME or MOTU interface plus a strong DAW where you can run latency as low as 2 ms to make for natural playing ... mind you then your MIDI latency is probably bigger than your audio latency so it'll be worthwhile to measure that (although here Roland often outperforms MOTU and alike)

Rob, what Roland interface was it that you were using? Live jamming through the PA was no issue for my drummer with a full band also being ran through 64 bit VST's, but he did complain about playing to the metronome specifically when recording with drums. I figured it was metronome timing denial on his part, lol. I was able to hold a beat to it when I tried it. How do I check to see the latency of it to get it under 2ms? I just want make sure I'm not terrorizing my drummer ears with unconfirmed latency, lol.

camgrah86
Rob, what Roland interface was it that you were using? Live jamming through the PA was no issue for my drummer with a full band also being ran through 64 bit VST's, but he did complain about playing to the metronome specifically when recording with drums. I figured it was metronome timing denial on his part, lol. I was able to hold a beat to it when I tried it. How do I check to see the latency of it to get it under 2ms? I just want make sure I'm not terrorizing my drummer ears with unconfirmed latency, lol.

I had used a VS-700 and an OctaCapture. Both with same results. BTW the latency Sonar reports for these units is correct (no hidden buffers like in other units which are not considered).
 
Like Johnny V said above. Jamming may be fine as all adopt to the drummer but being really tight on the click with a latency of 6-8 ms (which is what I used to get with the Rolands) will feel odd and tightness hard to achieve.