As far as I can see judging from that product screenshots on Simmarket, the scenery comes with its own custom jetways, meaning if you don't see them, it has nothing to do with GSX.
The LIMF_Jetways.bgl is also activated, but I still don't see any jetways.
GSX replacement jetways files should never be Enabled on 3rd party airports. If the scenery is named correctly according to the standard, GSX should have disabled it automatically, but if it's not, you are supposed to Disable it manually from the GSX Configuration page.
