I really all depends on the size of the venue. A lot of the smaller clubs here in this area won't mic the bass or guitar and rely on the stage cabinets for them. Usually that means you end up with a recording that has lots of vocals and lots of drums (which usually aren't mic'd very well).
Stage vocal microphones usually don't pick up the guitar and bass as well as you would think, so yes you'll hear some, but don't be surprised if you end up with a lot of vocals and little else on your tape.
The only real solution for this is using microphones in the audience and mixing the two sources OR just going with audience mics and forgetting about the board feed.
Then again, it could be the board has everything mic'd and you'll be fine.
Wayne