The ONLY requirement for riding the DME bus is that you have a WDW resort reservation. It can be a pkg, it can be room only, it can be DVC...doesn't matter. Just needs to be a resort reservation, at a WDW owned resort, that is active at the time you want to use the bus. And you need to reserve that ride in advance.
As long as you are staying at a Disney operated resort you can take DME. It is not available for Swan/Dolphin, SOG, the hotel plaza resorts across the street from DTD and the Bonnet Creek area resorts.