Oneworld lounge access is generally granted if one of the following is true

1. you have status that permits you to enter, i.e. sapphire or above, and you are holding an onward, oneworld airline boarding pass
2. your class of service on the transoceanic oneworld flight is J or above, and you are holding a oneworld airline boarding pass connecting to that flight within 24 hours.

As long as you are on an oneworld flight, and you meet one of the requirements above, you can enter a oneworld lounge. Whether the CX flight has AA numbers on it is not important.