True? Not really. One year I had to use a wheelchair at the park, and some rides (emphasis on some, not all) allow wheelchair users to enter the ride at the exit line. However, we still had to wait our turn for our party to be seated on the ride. It wasn't the same amount of time that we would have had to had we stood in the regular line, but it wasn't instant walk-on access.
Again, this is only with some of the rides/attractions. You can get a map from the wheelchair rental place that has a list.