Okay....you've really got to believe me on this....I truly do know what I'm talking about!!! Anyone, as long as they have an existing DME reservation, can ride the DME to, and from, their WDW owned resort!!! Everyone!!! The airline you arrive on, and depart on, makes no difference. 'Participating' airline matters only with RAC (Resort Airline Check-in) if you want to check your bags and get your boarding passes on your departure day. Other than that, it's not an issue.
The only times you would have to get your own luggage, upon arrival, would be if for some reason you didn't tag your bags with your yellow luggage tags when leaving home. Or, if you arrive at MCO after 10pm, prior to 5am. Some people like to get their own bags...so they don't tag their bags. That's their choice. Or if you arrive after, say, 6pm, and don't want to wait until close to 11pm to get the bags in your room. But, again, that's your choice. As long as you arrive between the hours of 5am-10pm, and have tagged your bags with your yellow DME luggage tags, before leaving home, you will be able to have the bags 'magically' appear in your resort room, up to 4 hrs after resort check-in.