There is no way of knowing whether he is faking the allergy story or not. I'm not a fan of his, but understand the seriousness of allergies and exercise/racing/etc. In some areas at varying times of the year I just can't ride hard, period. I don't know how to describe it, suffocation is a bit dramatic, but "hard to breathe" doesn't quite do it justice. I've learned to recognize it, back off and deal with it.
Medicine? Well, yes, there is a chance it can be abused. A lot of the drugs are stimulants that's why someone would claim allergies to get a TUE. But I'm not sure they're doing themselves any favors. I found some made me aggressive (okay a good thing for a racer), but I'd end up pushing myself more than I should. That's probably okay for a single day race, but not a GT (okay, hGH could help there, too

). They also can cause irregular heart rate, palpitations, etc.
I'm not a pro, didn't like the side effects, happy to take it easy when I have to. In my experience, I think it's entirely plausible that he has allergies that affect him only during part of the year and that he is legitimately taking something for them. He could also be making **** up. Who knows. In the grand scheme of things, I doubt they help him anymore than 3 cups of coffee and a few caffeine gels.