My problem is that apart from that all GSX vehicles are also displayed.
That's normal, and it's a shortcoming of that program that, instead of asking all kind of AI, should have used a Simconnect instruction to request *aircraft* AI only or, at least, have an option to let user select to see everything (aircraft, ground, boat, etc.) or just aircraft.
AES and FSX airport vehicles are not displayed.
That's normal too. AES vehicles are not really ground AI, but are created by AES in a way that FSX doesn't consider them to be ground AI, and FSX airport vehicles are not ground AI either, they are part of the "Living World", which is not "AI", so that's explains why the program that you use can't see them: the Simconnect call that ask for a list of AI will only interact with proper "AI", not just any object that moves.
Do you have any idea if it is possible to remove the GSX vehicles from appearing?
The only way is asking the developer of that program to change the Simconnect call used, and request only *aircraft* AI, if this was the intention of the product, there's no other way, and we can't fix it from our side.
As an example, the air radar that comes with the F/A-18 included in the Acceleration Pack (we made that one...), doesn't show GSX vehicles, because it correctly ask for aircraft AI only, not everything.