Thanks sbm12 and ijgordon!!

Follow-up questions:

My brother's full award flight routing will be RDU-EWR (Colgan), EWR-LHR (VS booked with CO flight no), LHR-BKK (TG), BKK-TPE (TG).

(1) When he checks in at RDU, will the CO check-in be able to check his bags all the way through to TPE and/or give him his boarding passes?

(2) Does the answer to (1) depend on whether the entire thing is booked as one reservation? Or can it be one reservation for RDU-EWR (EasyPass reward), with EWR-LHR-BKK-TPE (SaverPass reward) on a separate ticket? Will the staff at RDU know what to do to check his bags through to his VS and TG flights?

Thanks!