Making many assumptions here...
Point: A GFCI may be placed upstream of many other outlets, thereby making those other outlets GFCI protected.
Suggestion:
1. Go to distro panel and turn off the breaker for that circuit (GFCI-hottub).
2. Remove all "load" side wires from the problematic GFCI. Remove these wires from the box, or wire nut or tape them to avoid problems later.
3. While you have it out of the box, inspect the GFCI for burns, broken wires, etc.
4. Reinstall GFCI.
5. Turn breaker back on. Attempt to reset GFCI. If it won't reset, the GFCI is probably bad. I'd replace it.
6. If it will reset, there is a problem downstream, and each wire and device must be checked.
7. You can buy a device which will check a GFCI. I'm looking at one now, made by GB. Bought at Lowe's or Home Depot (bad memory) and cost about $9. But the GFCI must be able to reset before this will test it. It provides a simulated ground fault for the outlet, and if the GFCI is good, it will trip. If it won't trip, replace the GFCI (providing the tester is working- check on another GFCI).
Be very very careful (as you appear to be) when goofing around with 110v and hot tubs. 110v is very dangerous. Unlike higher voltages which will blow you off the voltage, 110 will hook you up and you can't get away.
My lawyer told me to say something about liability, but I told him it was a guy on AR15, so he said "Oh, those guys are careful!"
Good luck. Let me know if you have any more ??'s.