I don't know the Southwest info ... check out their website!
As for DME and tipping ....
If you use DME as designed, you won't have your luggage with you when you get to the DME bus at the airport. You WILL have carry-ons. You can bring your carry-ons on the bus with you (if they fit under your seat or on the overhead shelf), or the driver will stow them under the bus for you. If the DME driver touches any of your bags, then a tip would be appropriate. $1 per bag is pretty standard, but some people do $2 per bag. if the driver handled none of your luggage and didn't provide any other personalized service just for you, then the driver really doesn't expect a tip. I'm sure it would be appreciated, but under those circumstances it's not realy expected.
Believe it or not, you don't need to tip the person who brings you your DME-checked luggage, if you happen to be in the room when it arrives. because the service is designed so that you can be out and play and don't have to wait around for your bags to be delivered, Disney pre-tips the people for doing each DME baggage delivery.
On the way home, it depends what you do with your luggage. If you are flying one of the "participating" airlines, you can use Resort Airline Check-in and actually check your luggage at your resort (and then not see it again until your home airport). The people manning the RAC desk should be tipped, just as if you were using curbside check-in at the airport. And again, if the DME driver touches any of your bags, a tip is in order. Also, if you used Bell Services to take your bags from your room to the lobby, that person deserves a tip.
I hope this all makes sense.