Nowhere where the Jetway replacement files are discussed ( Page 7 of the GSX Pro manual ) it says you need to disable also the related Airport Service file for that airport.
At Page 8, where Airport Service are discussed, in addition to explain what they are and what they do, it's explained their relationship with 3rd party scenery and when you might want to decide to remove them. Short answer is:
- If the 3rd party scenery doesn't come with a custom Airport Service file, don't Disable the GSX Airport Services
- If the 3rd party scenery does have a custom Airport Service files, IT DEPENDS what it's used for.