If you know what gates belong to AA, you could use one of them, but the ATC system sends you to whatever gate it chooses. I fly AA myself, and frequently find myself sandwiched between either United or Southwest.
If you do not have any parking space left for AA yes ATC sends you to another spot. But if you assigned the right gates to AA and all the AI traffic have als the airline code "Parking: Gate AA" then it should work. At least with all my airports i have them on the correct parking spot. Only on rush hours when all gates are full there will be a mix up.