Stray voltage is an induced voltage caused by a spinning magnet (impeller for example) that is submerged in saltwater. To put it simply, a submerged pump with a spinning impeller acts as a small generator. Stray (induced) voltage has low to no current behind it and is easily handled by a ground probe. Many pumps with two prong plugs will cause stray voltage due to the lack of a grounding shield like the 3 prong pumps have.
Leaking or shorting voltage is caused by a failing item like a heater or pump. This voltage has A/C current that is being supplied by the wall socket. This type of voltage is dangerous and cannot be fixed by a ground probe. In this case, a ground probe completes the circuit and causes a bigger problem.
It seems that there is little current involved and most of the voltage is induced by the pump impeller actions and from any two wire immersed devices you might have.
But it also seems to me a probe isn't a bad idea, as a GFCI will detect and trip any significant current, the probe will keep the seawater at the same ground potential (voltage) as the house wiring has. But in the end, no one thinks even my 34 volts is a big deal on all the posts I have studied so far.