Bowwow, obviously the purpose of the Caterer is to book this program to make money. If people go to the hotel without booking through him and try to use his “accommodations” anyway, that would be infringing and imposing on him to cheat him out of his profit.
He would have a right to block you from the minyan since he has to pay for the rental of the room for each minyan, as well as the seforim, siddurim and sefer Torah. You are not talking about a local shul that is there whether this group and you come or not. The hotel does NOT give it to him for free. Every person in the program is paying for the use of the room for the minyanim within the fee for the program. Why do you think you have the right to infringe on their program and daven in their minyan for free?
So if this is your intention, the right thing to do is to call the caterer and ask him if that would be ok with him.