Sounds like a hack fixture if you ask me. What kind of ballast is it? T5/HO, due to their relative "newness" have ground connectors on the ballast itself, though most any electronic ballast will have a ground connection of some sort. The "green" wire in the line cord /household supply is an equipment ground, and all it really does is ground the ballast housing and the reflector/fixture housing in most cases. If the ballast has a plastic housing, there is no point to grounding the ballast... Grounding the reflectors is a somewhat ambiguous situation. On the one hand it is not a bad idea to ground the reflectors but on the other hand, it provides a path to ground between the tank water, through you, when touching the reflectors for whatever reason with a hand in the tank. GFCI don't care about that.
