How is this any more or less stupid than skydiving?
jumping into any body of water you are not completely sure is safe is a good way to end up on a spinal board.- it's called tombstoning in UK (the name probably came from the US) and costs several people their lives or mobility a year in UK.
These guys may well have done a thorough recce and checked for rocks and other underwater obstacles.
Were the FAA more interested in the low flying than the jumping in?
aa - I think you skydivers are barking mad jumping out of a serviceable aircraft but if that's what floats your boat
I've dropped plenty of parachutists from helicopters over the years but I still think it is tempting fate.