Is this really an industry standard? I don't recall ever seeing a listed lug for bonding wood. TBH, I have little experience with hot tubs as well, but this just struck me as odd. You are looking for the difference of potential from the wood to the water, it would appear.
I don't know if it is an industry standard.
IMHO if a person experiences a concerning shock, the first test is to use some instrument (which won't get injured) to measure what the person felt. If someone feels a shock from wood to water, then IMHO the first test is to measure the voltage from wood to water.
Now the _problem_ might be a lethal potential difference between soil and hot tub water, which is showing up as a minor but annoying voltage between wood and water because the wood is acting as a pretty good insulator. But the first step would be to measure from wood to water, and then trace from there.
-Jonathan