GSX can only remove airport vehicles that are Simbojects of the "Ground Vehicle" category, which can be added either by the simulator itself, as Airport Services and Living World vehicles. These will be removed by GSX automatically around the selected gate and can be controlled by the MSFS traffic sliders
However,. objects added inside the airport scenery files as static objects to add ground details, can't be removed dynamically by GSX, since they are not objects, but part of the scenery itself. The only way around them is to customize the gate and alter the GSX vehicles starting position trying not to clash into these objects.