BTW, if the GFCI is feeding a hot tub you really will need that grounding conductor. Hot tubs build a very significant capacitive coupling within the water which must be bled off to the ground rod/Ufer. I've measured over 50 Volts to ground!
I am not sure how you legally avoid it. There are references to "minimum 12ga insulated copper" EGCs all over 680.
I would like to see the bonding of plastic package spa's strengthened if we can't enforce a 3' minimum insulated deck around all of them. There is a conversation going as we speak over on usenet about a guy with a ground shift between his concrete patio and the Hot Springs plug in spa.
Not enough to trip the GFCI, just enough to tingle. Scary!
