Hi Brian.
I don’t think it’d affect BuddyPress. The users are still WordPress users, s2Member doesn’t change this, so BuddyPress can work normally.
The only interaction between s2Member and BuddyPress regarding users would be the custom profile fields each adds. BuddyPress has its own, which don’t integrate with s2Member’s pro-forms; s2Member has its own that that can be integrated with BuddyPress to a certain extent. [hilite path]Dashboard -› s2Member® -› General Options -› Registration/Profile Fields -> BuddyPress[/hilite]
I’d suggest that you create a test installation of wordpress, install BuddyPress and the plugins you have now, create a couple of users, then test out the migration to s2Member there. That way, any trouble that comes up will not affect your live site. And when you do work on the live one, remember to create good backups of everything so you can get it back up if anything goes wrong.
You don’t seem to need to migrate users, but just in case, here’s an article about that. Knowledge Base » How to Migrate to s2Member Pro from Other Software
I hope that helps. :)