According to what I am reading you are supposed to supply the readings to pass inspection but with two rods no readings need to be provided. I have no idea if that is accurate but I’m seeing that sentiment in several forums. Ultimately, I’ll just do whatever the inspector wants, but from what I am reading double rods seems very common if not required. But I have no practical experience here.
On new service installals or meter pan repair/replace you need 2 grounding rods. Different inspectors want different things on an outdoor sub panel. Rarely do they want a ground rod, but I've encountered it twice when the service was older and had a single service rod. This is not in NEC anywhere. Code states any sub panel to have seperate ground and nuetral bars and the ground bolt should not be installed in a sub panel. The only combination of nuetral and ground occurs in the main panel. The pools grounding and bonding never touch except in a UL listed Jbox with a 120v wet niche. No harm having the ground rod there and not using it. For using it on service It will not meet code that far apart I believe the double rod has to be 3ft max apart