I didn't stiff him. He did nothing deserving of a tip.
So, if you had a stroller, yes, he did in fact do something for you. He stowed and then removed that stroller. He is paid to drive the bus...period. He is not paid to be a baggage handler. So, yeah, you kind of did 'stiff him'.
When using DME, all tips are taken care of...unless you have something that has to be stowed beneath the bus. That can be a stroller, a car seat, a largish carryon bag..whatever. As soon as a driver 'touches' a bag, he is going to feel entitled to a tip. Whether or not you tip is completely up to you.
I have tipped DME bus drivers even when I had nothing stowed beneath the bus!! That driver was incredibly friendly, was very informative on the drive to WDW. He was just a joy to be around..he got $5 from me.
On the other hand?? I had one driver that never welcomed me to the bus, didn't utter one single word, other than to announce each resort as we approached it and.....wait for it....then he would get up and announce that gratuities are always gratefully accepted. yep, he actually said that...with the signage right behind him that states the same thing. Now...I had a larger than usual carryon bag with me that trip. And it had been stowed for me. I had my $5 in my pocket to tip..I was ready. But, after the general attitude I got from the driver (from MCO to the resort) and the statement about gratuities? He got nothing..not a penny!!! I will NOT be asked for a tip. Oh, and he wouldn't let anyone off the bus until he had all the stowed items removed.
So, yes, the driver will expect to be tipped if he/she stows something for you. I think most people are prepared to tip before they get on the bus, if they are planning on tipping anyway. If you get on a bus with only a $20 bill then it is safe to assume you weren't planning on tipping. However, the driver's attitude probably wasn't the best either.
The resort to park bus drivers aren't considered a tipped position. DME drivers are. It's as simple as that. And yes, although they have Disney outfits on, and Mickey is on the buses, they are still Mears buses and drivers. They contract out to Disney. I 'believe' the Disney buses, onsite, are driven by Disney employees.