I called Mears this morning, but ended up with all the phone transfers at the Magic Express. The policy is this:
Drivers are taught to welcome the guests to WDW and step off the bus allowing the passengers to follow behind them. Those with luggage will be helped by the driver and those with no luggage can go on into the resort and check in. Drivers are not allowed to keep passengers on the bus while they set up luggage outside at the resort or at the airport. Drivers are not allowed to solicit tips as tips to drivers are not required. You can tip a driver if you feel like he has gone out of his way to help you.
The busses should have no drivers signs requesting gratuities. The lady wasn't sure but didn't think there were any official signs on the bus requesting gratuities. Like she said, tips are not a requirement whether the drivers handle baggage or not.
She gave me a long website where passengers can go to if this is happening. I checked it out and ended up at the following site. If this is happening to you she suggested you report it on the site. I would think you would go to Contact us as I see no other way to get to them. You might find another way. If this happens to you get the number of the bus, the time of day, the day it happened and if possible the drivers name. This information is necessary for them to follow up on the complaint. The site is:
http://disneyworld.disney.go.com/