I got stung on this before here ;-)
If there is no electrical equipment to bond, I am not sure what you would bond the pipes to ... other than the normal 250.104 bonding.
After the death up in central Florida from energized steel framing (and the medicine cabinet) they are getting a little pickier about bonding in bathrooms. There really isn't much to bond tho, since we never see metal plumbing in 1&2 family.
I have thought about this since my l;ast spanking here and the only real rationale for a difference between a spa and a tub is the heater. That is a big difference. These are usually immersion heaters and there is a good opportunity to energize the water.
