So I took a look at this plugin and was able to get facebook set up. It works similarly to WPBB's, you login/register using facebook and then create a wordpress account. It then automatically logs you in to that wordpress account whereas WPBB's asks you to enter your password again first. You see WPBB uses wordpress's built in authentication system so aslong as the plugin does for the rest of the social networks they will be able to view your forums, post, reply, send messages, etc. If you're hoping to be able to allow those users to comment on the social networks on those topics, posts, etc I don't think it'll be possible unless it uses some on screen popup which allows you to comment on the link since WPBB is all built into a single wordpress page but uses unique links. I wasn't able to see or use any of the commenting for facebook with WPBB or wordpress itself, not sure why, might be because I'm using localhost.
Hopefully that's answered all your questions, I'd suggest installing it yourself and setting up the social networks that you want your users to be able to use and see how it works with wordpress and WPBB as I might be wrong and if you're not using localhost you might have better luck.