Which rides are wheelchair accessible for a non ambulatory person? Is the tram wheelchair accessible?

Yes they do. They also drive you down to the lower rides and drive you back up. Also you get first access to the rides.

This is what I found on their FAQ: How do you accommodate guests with disabilities? Universal Studios Hollywood prides itself on providing complete and convenient access for all our guests with disabilities. Many rides, shows, attractions, escalators and parking structures are designed to comfortably accommodate guests in wheelchairs and other disabilities. There are designated guests-with-disabilities entrances for all our attractions in the Park.