Originally Posted by srbrenna
You can earn AA miles on a BA flight (and vice versa) if it is booked with an AA flight number. So MAN - JFK on BA metal but booked with an AA flight prefix would earn miles. Our Lurker comfirmed this
here
You can also earn BA miles on the BA flight (MAN-JFK) when booked under the AA flight number. I tried this in January and the miles credited to my account (no tier bonus though as it appeared as the AA flight number and not BA). I didn't think this would work but I put my BA exec number in anyway just in case they were looking to move people further forward :-), I got full miles and 60 tier points.