FlyerTalk Evangelist
Join Date: Nov 2000
Location: Nashville -Past DL Plat, FO, WN-CP, various hotel programs
Programs: DL-MM, AA, SW w/companion,HiltonDiamond, Hyatt PLat, IHF Plat, Miles and Points Seeker
Posts: 11,074
Though some of the post lean towards "not gonna work", in the vast majority of cases it would be fine. People do it daily.
Personally, I would probably plan an overnight in DC in this case. There is an Air and Space Museum near the airport worth a half day. On our intl trips that might involved another carrier, we use it as an excuse to visit that city for a day.
If you do stick with WN - carry on sure would save a bunch. Have not been to IAD in quite some time... somebody should be able to confirm you stay airside between WN and UA - I think you can.