I have never been told by any agent so far that SWUs required the flight to be credited to AA. Infact the outbound was ba metal so that would NOT have applied in anycase...
I just applied a SWU to a friend who has a AA flight with a AY FF number that the agent had no problem with so if that is a rule then the EXP agents are not in the loop nor is that AA IT system, all of which is not news to me
At anyrate I wont have to worry about it anymore