Wirelessly posted (Mozilla/5.0 (Linux; Android 4.4.4; Nexus 5 Build/KTU84P) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/38.0.2125.114 Mobile Safari/537.36)
I can't speak to the US code part of the issue, but from experience on AA-coded flights, yes, AA will give you MVP benefits (bag, seats, etc) when traveling on an O fare.