Every time I've flown EY, its been ticketed as the AA Codeshare. But I've been in business and first on these flights. AFAIK, other than getting the miles (Award, EQM, and EQD's) there are no special benefits bestowed upon AA elites on these flights. If you are flying up front, you don't need it anyway. But in the back, you won't be given anything special (extra bags, priority bags, lounge access, pre boarding, etc.)