The electrician is absolutely correct.

EITHER a GFI breaker or outlet, but not both. They do the same exact thing, it's just where the GFI is located. I like it as a breaker in the box because you KNOW it shuts down all the wiring from the breaker box out, whereas the outlet leaves the wires attached to it live.

And, for 20amp, you'll almost certainly need it to be the breaker anyway. I don't think they make a 20a GFI outlet--or if they do, it's harder to come by than a 20a GFI breaker.

As for the ground and rod, check with the electrician again and ask him about "banding" the pool. There may be a better way to do it other than a grounding rod--there usually is. It probably should be something called an "electrical ground" and not a "mechanical ground". The difference is that the EG is wired and the MG is to something like metal conduit or pipes.

Hope this helps.