Generally, it is the same hourly rate, for the same chain of gyms. However, if it is a popular instructor and the gym has hired the instructor to boost membership, they gym will have to pay the instructor more than they pay their other instructors.
Gyms has operating budgets and generally operate within those limits.
Maybe I don’t completely understand the question, but isn’t group cycling just another form of group exercise or training? If it is, I’m not sure what the basis would be to pay the instructor more unless of course it was based on experience, reputation etc. That being said, perhaps because Spinning is a specific trademarked certification, the instructor could/would be paid more simply because of the laws of supply and demand.
I believe it depends on the type of gym/studio you work at….I have seen gyms that pay GX instructors the same as spin instructors (and even consider spin classes as part of GX because it is still a group lead class where you need a certification to teach), but I have also seen spin instructors get paid more if they are specifically working in a cycle studio only.