Neither AES or GSX will do anything until you activate their services via their respective hotkey-activated menus.
Not really, in GSX, if you press its hotkey while parked, nothing will happen until you select an actual operation (Boarding, Deboarding, Pushback) from the menu. Pressing the hotkey again, to let the menu disappear, it's the same as having changed your mind without doing nothing. No objects will ever be created on the parking if you just open and then close its menu.
In AES, as soon as you are on a parking with engines off and activate the parking brakes, the parking is prepared with ground objects and stairs automatically approach the airplane even before you open its menu with the hotkey.
This difference is what prevents a better mix of both products because, if AES did the same as GSX, and created or at least started to move objects towards the airplane only after you selected one of its operations, you could do something like letting AES operating the jetway, Deboarding baggage with GSX, ask AES for lavatory/water vehicles, ask for GSX catering, and maybe being Pushed back by AES.
There might be some clashing between ground objects starting positions, but we can tweak that easily, it wouldn't be a great issue if you had both AES and GSX vehicles together at the same parking standing still, as long they aren't really on top of each other.
However to me it would also make sense to exclude any AES activated airports from GSX using the "Couatladdons.ini" file as explained in the manual, by adding their ICAOs to the "disable_on_airports" line.
We added that option for the only reason to give a temporary working solution to AES users wanting to use AES on an airport they purchased credits for.