A FlyerTalk Posting Legend
Join Date: Jul 2002
Location: MCI
Programs: AA Gold 1MM, AS MVP, UA Silver, WN A-List, Marriott LT Titanium, HH Diamond
Posts: 53,012
Not under this particular promotion, but I've flown into ORD on UA and ORD-Podunk on a United Express flight and had it all count for miles and bonuses with no problems.
If your commuter flight is something bizarre, I would still think that DCA-ORD-DCA on United would count as a roundtrip, but I don't know. Might depend on how it's ticketed...