Two things going on. One, there is no such thing as a participating airline in DME. All Disney resort guests coming in to MCO can use all incoming DME services, including luggage transfers and motorcoach transport, regardless of the airline they fly on. In addition, all Disney resort guests can use DME motorcoach service on their trip back to the airport. That's been true from day one of DME.
Second, the participating airline thing only applies to the Resort Airline Check-in service which allows you to check bags and get boarding passes at your resort. SWA was one of the few airlines that was not a participant in RAC and it still isn't listed as an official participant even though SWA passengers staying at every WDW resort except for OKW and CBR can now use RAC.
So, WDW guests flying on SWA can use all DME services and those at all resorts but OKW and CBR also can use RAC now. Indications are that OKW may be ready soon and CBR could be ready by the end of the year.