The PassPorter site is incorrect!! I was just at WDW, at BW, and did indeed ask the RAC CMs if there was any truth to this. I was told 'No...there is no talk about SW being a participating airline at all resorts at the moment. It will happen, for sure, but no one knows when that will be.'
The issue is that Disney combines DME with RAC...and they are two different entities. So, when Disney states that SW is not a 'participating airline' with DME, it gives the wrong impression. Add to that the CMs who give out incorrect info....'Oh, you're flying in on SW..you'll have to get your own bags and bring them to the DME bus with you.' is so very wrong!!! But, TAs and Disney CMs are telling guests that, so the guest figures it must be true!!
As of this moment....SW passengers are able to check their luggage at Pop, and the All Star resorts, no place else!!! You have to be staying at the resort, so don't think you can take a cab over to POP from BW and get your bags checked!!!