Marie
Following as well. Almost none of our organziations (we're a consortium) use Tessitura for any volunteer management, although I keep hoping we'll dive in soon.
I think (but have not tried yet, see above note re: diving in) that you could use rankings to restrict volunteer access to certain positions, assuming those positions are set up as performances. You could put the "must pass background" performances in a mode of sale that only the volunteers who have a successful background check (and appropriate ranking to indicate that) could access those positions.