Nah, no to Swellow. It may be fast as hell, but it's fragile, lacks good resistances, has only decent-poor coverage, and outside of Facade and Brave Bird, it actually doesn't really do that much damage. All Swellow does is call Tyranitar (who still takes pitiful damage from U-turn), Metagross, Skarmory, Ferrothorn and Forretress (on the Facade), etc in and give them free set-up opportunities. Plus, they can all take a neutral hit and OHKO back in return.
I admit that Swellow, if switched in on something it threatens and is able to activate its Flame Orb, can devastate certain offensive teams given that their Choice Scarfer or priority user is out of question. Swellow can do great damage to slower offensive mons such as Latios, Virizion, Celebi, and Darmanitan, but it's also doing huge damage to itself in return due to burn, Brave Bird recoil, and whatnot. Vulnerability to Stealth Rock and sandstorm also does a number to this bird.
So, Swellow's cool, but not really in OU. If I had some kind of list for RU, Swellow would probably be there.
edit: note to self, add gastrodon.