Two years ago, my wife was on an extremely restrictive diet. (No Gluten, Corn, nuts, fruits, dairy - no oils except natural animal fats or olive oil - and quite a few others ..... don't ask, even the doctors were at a loss) ... our trip to universal was fantastic. Almost every restaurant was extremely accommodating.
Now the year before that, a couple restaurants had a limited selection (Mama Della's concocted fantastic meals for her from their pantry) - but the executive chef at Margaritaville told us that if we had called at least a week ahead, he could have made sure that he had more things to work with to give her some variety beyond a hamburger with no bun. >>>Many of the restaurants (Margaritaville, Pat O'Briens, etc) got their chicken breasts in marinade from the supplier, so even a grilled chicken breast wasn't an option.
... so anyway, 2 years ago we called ahead to about 5 or 6 of our favorite restaurants and spoke directly to the executive chef at each one. We did that about 2 or 3 weeks before our visit. True to their promise, they all were extremely accommodating. They brought in custom proteins and ingredients to have on hand for the 8 days we were there. She never ate so well and had a tremendous variety of meals throughout our stay.
Bottom line: That open letter from Steve Jayson posted earlier is not just marketing spin. They really will go out of their way to deal with a wide variety of dietary restrictions. Just don't expect them all to be able to do it straight from their normal stocked pantry - except for the most basic selections for the most common allergies.