("Besides NM is not permitted to installed in a wet location such as an underground raceway".)
This is not run under ground. It will only run from the top of the panel up to the attic in emt with w/p conn, through the attic, then 90 out down to the disc, then liquid-tite to the spa.
What would be the difference between that and an outdoor breaker panel having NM run to all the circuits, (which is how they are all done here in AZ).
The Golden Rule - "The man with the gold makes the rule"