No. They can direct you, but they are not supposed to drive it on for you. If you have another member of your party who would like to drive it on for you, they would be able to.
Also, the older buses that have lifts require you to back onto the lift. You should be able to drive straight forward onto the newer buses that have ramps. There is some information in the disABILITIES FAQs thread near the top of the board.