There are several of the major rental companies located on site or in the DTD area. Most will pick you up at your resort and bring you to rental location and return you to your resort upon return of to car.
A few of the companies are, Alamo/National, Hertz, Dollar & Budget, the closest to the All Star resorts would be Alamo at the Dolphin Hotel, or at the Car Care Center. The CCC will pick you up, that service is not available from the Dolphin.