If the metal fixture is attached to steel or copper pipe, it's grounded through that pipe. If the metal fixture is attached to plastic pipe, it's not a path to ground, and is also safe. Safer, really; there's no chance of something like that becoming energized, so it's not a potential shock risk from that standpoint, either, and is as safe to the bather as if it were plastic.
Makes perfect sense, actually.
The requirement in Section 680.74 is to establish equipotential bonding at and directly around the hydro-tub in order to reduce the protential of voltage gradients. It really has nothing to do with grounding or establishing an effective fault path to clear unitentionally energized parts.
680.26(B)(3) I think applies here
Ob
Hydromassage bathtubs need only meet the requirements of Part VII. of Article 680. The section you reference would not apply. See Section 680.70
