If you note it on the reservation, they will be more accommodating. As someone who doesn't eat pork, I usually find breakfast buffets to be a bad deal, even with the other offerings. Maybe I don't want 3 mini croissants, a danish, half a bagel and some fruit for balance.
Anyway, check out Storyteller's in GCH. They have a buffet, but also a regular menu, so there is more to alter. But again, note that you're vegan on the reservation so that they're prepared to have a chef speak to you.