Well, this is explained in the manual ( Page 11, in the blue box ), GSX doesn't change, doesn't interact or controls jetways in any way. They will continue to work or not work just as before you installed it.
Which means, if the scenery has FSX jetways, they will continue to work (not always so well) just like before you installed GSX, and if the scenery have static jetways or jetways animated with other ways, they will continue to be static or work as they were before GSX.