I don't think only certain MBTI types can be in poly relationships, but I think the MBTI is an important indicator of how people will respond and handle the relationship and whatever problems come up.
I happen to be an INTJ, and very proud of that. ;-) We're pretty rare. The man in our quad is an ISFJ, so we are on the same wavelength fairly regularly. Sometimes he gets a bit more hung up on facts and evidence when I can grant assumptions a bit more easily (S/N), and he is definitely more of an emotional arguer than a logical one (F/T), and that's how our differences crop up.
Then there's the other half, with the complimentary personality type:
My lady love, as well as the third (whom I'm not in a relationship with) are both ENFP. They need constant social interaction, which means neither actually deals that great with the triad, because if either spends time with the man of their life, the other feels left out, bored, etc. I'm a bit nervous to be the only T in the house!