Can confirm AA elites can access the 51st and Green lounge when traveling on Aer Lingus. As for seat assignments, I was auto-assigned a window seat near the front of coach at OLCI with no ability to change. I asked the lounge attendant at the LHR EI lounge if I could get an aisle seat anywhere on the plane and was accommodated with an aisle seat near the front for no charge. No idea if AA status had anything to do with it.