While I have heard people say that this is done for some allergies, this is not always offered for foods when you are dealing with peanut and tree nut allergies - which is what my child has. In a buffet restaurant, the chef always walks us through the buffet line and tells us what is and isn't safe. Generally only the breads and desserts aren't safe - and it is almost always a cross-contamination issue vs. the items actually containing nuts. I will ask for an alternative bread and dessert to be prepared in the kitchen, but we've always eaten off the buffet line.
At Disney, they seem to avoid putting peanuts and tree nuts in most of their items, and once the chef learns that we are "just" dealing with those two allergens, they typically say something like "that's easy" - meaning there isn't that much to worry about (relatively speaking vs. other multiple food allergies) in their restaurant. They definitely take it seriously. Hope you have a great trip!