Julie,
that depends on how the contract is written. I always stipulate that I can enter my own dogs in Specialties that I shoot although I rarely show them myself. The only times I get brought into service is when my handler wins virtually every class and there are only so many handlers to take in her non-priority dogs. Since Rowdy shows well for me (my knee problems notwithstanding -- I've put a Group 2 on him) we felt he had the best chance with me on him. But that's unusual.
Keep in mind that the only dog we showed in Miami was our Veteran so nobody had a problem with that anyway. If I was showing dogs in every class as well as BOB, that would be a different story and I wouldn't do it. In fact, when Linda was co-Chair for the 2007 Rottie National here in Florida, the only dogs we showed were our two Veterans.
But, there are not rules against it any more than there are rules against Show Chairs showing their dogs. In small Specialties, if the Show Committee didn't enter their dogs, they wouldn't make 2 pts let alone a major.
Jim