I don't think anyone in the NW board could specifically answer a question as to what AA would do. I think you need to call AA and ask what happens if you fly another carrier on the outbound, would you be protected on the return? NWA has no control over what AA does or does not honor. Supposing that I or another passenger had some success in the past with your scenario is no indication that is what AA would do tomorrow.

BUMP (bring us more passengers, i think is what it means) also is supposedly not a very well know program at the ticket counters. I don't think it was intended so that you could buy tickets on one carrier and fly on another at will. I think it is intended more for "emegency" or "one time favors" type of things.