Yep, that’s possible. As Bowe said, you can check out my plugin at test.jobboardr.com. The plugin works on the bleeding edge version of BuddyPress, though, which has been a long time in the works. That’s the main reason why it’s not available yet. I’ll def. make it compatible with 1.2.6 and then release it.
As for the marketplace, I coded a shopping cart that integrates with groups, so it’s definitely possible. It’s quite complex, so you’ll probably want to hire a developer to do it for you, as I can’t release my code to the public.