I jumpseat SWA all the time. They folks @ SWA are awsome. The pilots and gate agents are very friendly. I never go in pre-board unless I am told to do so. I get about 50-50 on pre-board. I do not care if I am the last to board, because my commute is only 35 minutes wheels up to wheels down. I will gladly sit in the middle seat for the ride.
As for uniform, you do not need it for the jumpseat privlidge.