is it really all that dangerous? A little tingling never killed nobody.

Well, I guess we would never find out if they guy that got killed felt
just "a litle tingling" or not, cuz he's dead.

I'm actually having a hard time thinking of a scenario that would
significantly energize the pool without triping the GFCI or the breaker.

Here's an easy one; supply line. He said that both GFCI breakers were
near the pool. If the previous owner is as stupid as it seems, the
incoming line that supplies power to the two breakers is probably not
GFCI at the main panel. A nick in this line would energize the pool if
it were close enough, or if the soil types were such that the path
through ground water or pipes to the pool then to ground was best.

-Kevin