Its possible that companies like Ryder have air-ride vehicles, but I kind of doubt that its standard. I would never transport art in a rented vehicle like that unless I had to. But I guess it depends on what the art is. Im not sure what you are transporting, but think of delicate paper works. A few good bumps could easily seperate it from the mat or backing.

If you use a good art shipping company, not rent vans on your own, you should have air ride, full climate control, gps tracking on the vehicle, and dual drivers. This is what our museum uses (and most museums I assume) in almost all cases. Thats standard.