How urgent is it for you to get your baggage?

If it's not urgent:

Since there's not PPBM for domestic flights, if the bag is through-tagged and you drop it for recheck it should make it to your destination even if it's not on the tagged flight and even if you don't make that flight, though UA would likely tell you that you're responsible for retrieving it from the airport.

The risk is if anything goes wrong since the other ticket is wholly unrelated the IATA Final Delivering Carrier rule gets murky -- the OAL BSO probably won't be able to help and the UAL BSO will be confused about how you got there.

You may be better off if the connection gets blown letting/asking the transfer desk or UC to rebook you on the alternative out of DCA... They'll send your (rechecked) bag to the landside baggage claim for you to grab and bring to DCA and you won't have to buy the 2nd ticket. It's not the most fun way to connect but I've done it (IAD Silver Line -> Blue/Yellow Line DCA is a bit monotonous but not very expensive; of course taxi/uber also works but I'm not convinced its substantially faster depending on time of day)