Article 680, which covers pools, has a 'spa and hot tub' section that modifies the pool rules.
It's a good idea that he also check with the local town, as local interpretations - especially regarding whether the ground wire need be insulated - vary. It's possible the town will want an insulated ground wire all the way back to the main panel ... which rules out NMC as a wiring method.
If there's a gazebo over the thing, a ground rod, in addition to the ground wire, is also a good idea. Again, this is a matter of some discussion.
Wires need to be buried deep - preferably 2 ft down. Getting into design issues, I prefer pipe. These steps protect against the gardener damaging them when working on the lawn sprinklers.
Finally, there is the matter of disconnect location. Putting it in the enclosed area that also hides the air conditioner is a common error. An "emergency stop" is not required for residential tubs.
