They do offer them, but they must be rented at each individual park. They cannot be taken from the Studios to IOA or to CityWalk. You can rent a standard manual wheelchair at the hub which can be taken from park to park but you'd have to push!
If you'll be renting a car, the perfect solution is to rent a
scooter for the length of your stay. One year, my husband had foot surgery and couldn't walk long distances. We rented a scooter from
Walker Mobility and were very pleased. I would highly recommend them. They deliver the scooter directly to your hotel. It comes apart easily to be stored in the trunk of a rental car. You just have to bring the battery up to your hotel room each night and plug it in for a charge. The charge got us through the whole day and we were able to take the scooter everywhere, from park to park, to CityWalk and even on the boats to the Universal hotels. It worked out very well for us.
Of course, if you're not renting a car, this isn't possible.