I think we're on the same page. What I refer to as the "wet niche" is a stainless steel cannister (your "forming shell") that the Pentair light assembly fits into. The trick is that the niche is already installed, attached to the pool wall, covered by a concrete deck, diving board, etc. I can't really tear up the entire deck to prove that the #8 grounding wire is attached to rear of that niche. However, that's why I tested the continuity between that grounding stake and the front of the wet niche that I can access. Since it has continuity, I have to assume that the rear connection is intact. Is that conclusion safe, or would that be the case for any metal housing that comes in contact with the earth?
As for being tied to the "bonding grid", does that refer to what I call the grounding loop that attaches to the metal wall braces, ladder insert cups, etc.? If so, I know of at least one independent location where I could test for continuity between that ground loop and either the stake next to the junction box or the niche itself.
I try to be conscientious about safety, so I appreciate the help. It sounds to me like I'm covering all the bases that can be tested, but it sure helps to hear a second opinion.
PS: Which item provides more protection -- the grounding wire or the GFI? And as an engineer, can you tell me in layman's terms why the grounding wire for the niche serves a different purpose than the grounding wire for the light?