GSX supports only the user airplane.
AI traffic is already very heavy on fps on its own, if each parking AI were to be serviced by GSX vehicles, it would probably amount like having 4x the amount of AI you already have so, assuming it would even fit in memory ( it probably won't ), it will lower your fps to unusable levels. Not even mentioning all the traffic deadlocks of so many vehicles travelling around the airport, both between themselves and between them and the taxiing AIs. Simply not doable.
