I've been in two kink based, power exchange type, poly relationships. They had no impact on the poly side at all. We decided beforehand that no tasks etc would affect my other relationships, that's just a douche move. Other than that, it has no bearing on anything. I call him "Daddy".
I don't make the huge differentiation between sub and slave because I know subs with rigid, strict protocol and I know slaves who don't. Nobody is doing it wrong, per se, it's just that kink based relationships are like any relationships, totally individual. I would be someone's slave but that wouldn't mean that they could impose restrictions that are unethical to my other partners without their willing consent. I wouldn't be with someone who behaves so unethically. I'd also have two or more Dominants if i felt they could all work in co operation.