In short...it doesn't matter how you arrive at MCO...the airline doesn't matter, nothing matters. All that matters is that you are at MCO, you are staying at a WDW owned resort, and you are listed on the room reservation. That's it. And of course, you must have a reservation, made before you left home, for DME.
If you tag your bags, with the yellow DME tags, your bags will go directly from the plane to your resort..provided you arrive between 7am and 10pm. If you arrive between those times, you will have to retrieve your own bags.
A note...Shades of Green and the S/D are not Disney owned resorts, so not included in the DME perk.
When it's time to head back to MCO, from your WDW owned resort, you get to again ride the DME bus...as long as you have your reservation. IF you are flying a 'participating airline' you can check your bags at the resort, get your boarding pass...all before you leave WDW. This is not DME, it is RAC (remote airline checkin). You don't even need to be riding DME back to the airport!!! You just need to be flying on a 'participating airline'. And yes, SW is doing a test run of providing RAC (remote airline checkin) at POP. Here's hoping it goes well and they offer it at the other resorts...making SW a 'participating airline'!!