As many folks pointed out this should be solid but Your Mileage May Vary. Evidently the pool guy and the AHJ have an understanding. ... or perhaps we have a misunderstanding about what this wire is.
The "insulated" #8 that may be stranded is the wire from the forming shell to the Junction box for a wet niche inside a PVC raceway. Maybe someone has decided that is also any other wire from the forming shell. The reason this wire is supposed to be insulated is it runs through pool water for most of it's length. The raceway from a wet niche to the Jbox is underwater up to the water level. That is why we pot the niche end and pot the box if it isn't 8" above maximum water level.
