I'd like to thank you for posting your experience--it is good to know that a dog can be in the cabin or hotel room as a matter of necessity-
Anyway, my youngest son has an extreme allergy to most animals--he instantly gets hives, his eyes and face swell shut, and he has trouble breathing But what are the chances that we'd ever be on a plane with a service dog . . . And what is the official policy for animals in an airplane--obviously it can be permitted for wants as well as needs--any airline officials out there?
My kids have service dogs. We travel on airplanes regularly. If your son is as allergic as you describe he's likely to have problems in school and in many public places. If you have severe issues you're likely to react to the dander on people's clothing. Do you have an IEP for him at school? Take the epi pen everywhere?
There are not requirements to accommodate a dog allergy unless it's enough to be a disability. Most allergies are not that severe. I have tons of allergies and they are not insignificant (I also use an epi pen) but I am not disabled by them. I'd be sure to let the airline and any hotel know in advance that there is a significant allergy issue.