For the international conventions that US delegates are invited to, they are completely on their own as far as making travel arrangements.
However, there is a list of "approved" hotels. Delegates must stay at one of the approved hotels, and must stay for a fixed minimum / maximum number of nights (I don't recall the exact details now - I think it is something like a minimum of 5 nights and a maximum of 9 or something like that).
I've seen some of the prices of the hotels. They ain't cheap! The ones I recall are well north of $200 per night.