I spent a while poking around (and by that I mean, I spent a few days' worth of free time inhaling several months' worth of discussions) on swingers' forums when I was in a relationship with a bi guy. I really got the impression that swingers weren't terribly accepting at all. I had started off with curiosity (because hey, informed consenting sex with lots of variety while maintaining a loving relationship as a priority, great right?), but wound up pretty unnerved by their lack of acceptance as a community for many kinks outside their own. The general rule (of course I'm sure there are exceptions, I'm just explaining the vibe I got from the "cumulative average" of the sites I read), but it really did seem that a lot of the men would feel threatened by being in the presence of a bi male.
Made me kind of sad. I'm not really in the swinger community's age range, though, and perhaps there's room for people my age to come up with a more inclusive community.