I do know of a Dom with two live in submissives. This to me is a polyamorous relationship.

They have been together for about 4 years now, and their dynamic is very interesting to watch. He does Dot over them both, yet there is a hierarchy for them.

I believe there is a thread on here talking about poly relationships, but since I wasn't able to find it.

http://www. xeromag.com/fvpoly.html