If you can find an airport that SWA serves, you can bet that United would match SWA's fares. They do in Louisville and Nashville where SWA serves. United pricing in Lexington, where SWA does not serve, is 2-3 times as high as Louisville and Lexington.
Editing to add:
I just looked on SWA's website, hoping they would open my travel dates (late June). They have not, yet, of course. However, I did notice they serve Portland. I don't know your travel dates, but I looked at several dates in the next 3 months or so, and flights from Portland to Orlando. Though some of them were booked solid, I saw several one way fares for about $100. Round trip would be about $200. If it were me, I'd forego the free United ticket and go with SWA. Even paying for 2 people, the total SWA r/t fare would probably be less than the one United r/t fare. You could save the United free ticket for some future time when you have to travel to some city that doesn't have SWA, and/or you can't find bargains like that.