I have had good experiences working with DCA check in agents re: check through luggage.
I just had them check my luggage through to TPE (KE) via JFK on 2 separate ticket 2 weeks ago. Depends on who you get, some may not have as much experience with it and give yourself extra time for the process just in case. It took her about an hour to get mine done because she had to get her supervisor to help.