So I'm not totally sure what you're trying to do. You talk of dragging a loop from AD2 onto a track and playing it. Which is a midi track triggering AD2.
Then you say "yet if I press play and record it, records nothing." So if you press record (pressing play isn't ever going to record anything) I'm not sure what you're trying to record. Are you trying to record the output of the AD2 loop you're playing to an audio track?
Later on you say you're trying to record your yamaha DTX700 electric drums.. I'm confused, but I'll take a shot that what you're really trying to do is record your electronic drums. And I'll guess that you're trying to record midi from your electronic kit and have that trigger AD2 sounds.
If that's the case, you need to connect the midi out of your DTX to the midi in of your recording interface. Then in Sonar create a midi track. On the midi track, select the input to be the DTX and arm that track for recording.
Hit record and play your drums. You should record midi on your track from your DTX. Now insert your AD2 soft synth, but don't select simple track, I just select "synth track folder" "first synth audio output" "synth property page" and that's pretty much it.
Now on your midi track where you recorded your kit, set the output to go to the Addictive Drums synth. There are some midi maps for yam gear but I don't see the DTX, maybe it's a yam generic or something. You may have to move notes around in your midi track for them to trigger the correct kit piece. In AD2, you can hit the ? and go to "map window" to see the midi notes corresponding to the kit pieces. Make sure you're midi notes are assigned correctly and you should be good.
Hit play and your midi should play your AD2 kit.
gabo