As someone who has an uncommon food allergy, I understand your frustration. I am allergic to ginger, also not life threatening but I end up in the ER having to get IV Benadryl and epinephrine to get rid of head to toe hives. That wouldn't be the way I would want to spend a day of my WDW vacation. The problem with having less common allergies is often when you ask someone in the restaurant if a dish contains ginger you get a puzzled "I don't think so" answer and the person somehow thinks that is good enough. For some reason I have found that if it's not a peanut allergy (or something else more well know) people seem to think you can just take a chance or something.
One problem that many people who don't have allergies don't think about is that when you are trying to decide where to eat it isn't just a matter of determining what you CAN'T eat, it is important to know what you CAN eat. That's where I agree that it would be nice to know ingredients prior to booking so you can decide if you will actually ENJOY any of the options you are left with. It would be a serious bummer if you got there and discovered you don't like any of the options available to you.
I will say, however that as long as you do some advance planning it really isn't much of problem at WDW because you can always just cancel the ADR if you decide that it won't work for you after speaking to someone. Disney is one of the places I have received service that went above and beyond what I expected in dealing with my allergy. When we went to Trader Sam's I had no way of knowing what had ginger (I have to assume most Asian and Thanksgiving holiday items contain ginger unless told otherwise) our CM had the chef come out and talk to me. Not only did he tell me what did and did not have ginger, he also gave me recommendations on the dishes he thought were the tastiest options for me. He was awesome - in fact I wrote a commendation for him. When I told him that I often take Benadryl whenever I eat somewhere with Asian food, even if I am told something won't have ginger (since things are still prepared near it) he said he didn't think being Benadryled sounded like a very fun way to spend our day so he ensured me I wouldn't need to medicate myself since he was aware of my allergy.
