I agree with the above poster that it's not necessary or expected for you to tip the DME driver if he did nothing PERSONALIZED for you. If he didn't touch any of your bags and didn't answer any questions you asked, then I just don't think a tip is required or expected. Sure, it would be nice, but ....
OP, it's also important for you to know that Disney "pre-tips" the Bell Services CMs for delivering your checked DME bags to your resort room (we've been told on this board that WDW calls it a "GTY rate"). They do this because those bags will "magically appear" inside your room whether you're there or not, so this way the CM gets a "tip" whether you're in the room or there's an empty room. Just with human nature in mind, I imagine the DME luggage delivery wouldn't run so smoothly if the Bell Services CMs (who may be are nice people but after all are still human) thought there was a good chance they weren't going to be tipped for lugging that luggage up to the room.
When you check out of your room, if you get assistance with your luggage you should tip the CM who helped you. Getting your luggage from your room to the bus or Resort Airline Check-In desk is NOT a part of the DME service.