The default jetways in default airports (on parkings that have jetways, of course) will move, provided you have the "Advanced Anmimations" flag enabled in the FSX Graphic settings, and your airplane has its exits correctly set in the [Exits] section of its aircraft.cfg file.
They might not always move perfectly, and sometimes they might not even move at all, depending how you parked and your airplane model, and this won't change a bit if you install or not GSX so, your question doesn't really have anything to do with GSX, it's more like a general FSX question.
As explained on the manual, nothing in GSX will change anything in relationship with the usage or the behavior of the default jetways, they will continue to work (good or bad or not at all), exactly as they were before installing GSX.
