a.) All do. All Social Marketplace does is hook into BuddyPress for private messages. Forums are bbPress. Those are both free plugins, that work with pretty much any theme. Now, Social Marketplace has more features than just letting your customers private message each other, they make the interface to do so sexy and add other features too. But strictly messages-speaking, any theme is fine with BuddyPress. Some people love Social Marketplace (I’m one of them). Some people hate Social Marketplace because their support is slow (like, snail racing a turtle slow). But if you know anything about how to use a theme you’ll be fine. Those that have no idea are not fine.
b.) We dont test with themes. It’s up to themes to be compatible with WooCommerce. If your theme is WooCommerce compatible, 100%, then so is WC Vendors and all other WooCommerce plugins and such.