I understand the earth can be a ground path and the whole pool, spa, screen cage, deck, pumps and cover may be somewhere above zero volts compared to some theoretical ground but it will all be the same amount above zero volts if everything is bonded together.
680.26(A) says it all
680.26 Equipotential Bonding.
(A) Performance. The equipotential bonding required by this section shall be installed to reduce voltage gradients in the pool area.
"Ground" is really pretty meaningless anyway. I have seen 35v between the ground electrode systems of 2 buildings (on my Dranitz). We ended up bonding them together to stop stuff from blowing up when we strung data cables between them.
