We got a "pass" or whatever it's called, at Universal with no problem. I showed them a card that I had that said that this child has autism and can't tolerate waiting in long lines, and they gave me a pass.
We were there in Nov., and this was the first part of our vacation. My husband was very uncomfortable with the idea of getting special privileges so we only used it if the line was very long, so not very often!
A couple of us had an old "park-hopper pass" to Universal Studios that still had a day left on it (the rest had gotten lost!), so we left Islands of Adventure for a while and went to regular Universal for a while, and used the pass there. At MIB, the lines were quite long and they waved us over to the FastPass line (or whatever they call it there).
At Back to the Future, the lines were also long. We showed them our pass and they had us walk up a back way to the third floor and go in a door, and poof we were at the front of the line. That one made me very uncomfortable, as it was obvious to everyone standing in their spots ready to get in the next cars, that we had completely bypassed the line.
So yes, from my experience, they do have a special assistance card. As for wheelchair stuff, I have no personal experience but I'm sorry for the bad times that some have had.