Well, as far as cross contamination (cc) goes, I have never been 'glutened' at any Disney location. As a rule, they have been knowledgeable and concerned about cc and are more than willing to appease any anxiety. But as you probably do, if I run into a CM that either doesn't know or appears not to care I turn around and walk away because it's not worth taking the chance. And that has only happened ONCE.
As far as the disclaimer, most places that accommodate and have good prep practices will still have the same type of legal disclaimer to avoid potential legal problems. Accidents do happen and there are people who will intentionally claim cc to try to sue & collect damages. That being said, I will note that my being 'glutened' while very unpleasant & painful, is a world away from anaphylactic shock from shellfish, so I can certainly understand your being doubly concerned. Things I have found helpful are;
Peruse the menu online if you can. I find it helpful if I can plan ahead 1 or 2 choices that appear to be either 'ok' or would be easy to adjust to meet my/your needs.
Speak to the head chef or kitchen manager. Stress and express any concerns about their allergy prep practices.
Eat at 'odd' times, meaning less busy. I usually try to eat right when they open and (hopefully) the kitchen and ingredients are fresh & hopefully separate, and haven't accidentally been too 'gotten in to' to fix other customer's meals. Of course, that usually means eating lunch at 11 and dinner at 4.