As a guy who routinely teaches classes in rather dynamic environments and who's done this trip several times I can say that this whirly was something else! Most whirlpools dissipate as the travel down the eddyline and will spit you out after toying with you a bit. This one had the boat spinning around so fast that all I wanted to do was stay away from it
I don't know if this one would've pulled Dave down in spite of his PFD, but I can say that some folks in the UK took a mansized dummy, put a PFD on it along with a depth gauge and timer and chucked it into the Corryvrecken, a Huge whirlpool off of the Isle of Jur. While I can't give you the actual numbers (I can't find the data) but I can tell you that it went down a few hundred feet and finally came back up something like a 1/4 mile away and was down for about 15 minutes.
Regarding rescues: Think about the suction required to pull you down, in spite of the PFD. Without being on land, especially in a location where it's all I can do just to stay clear of the whirling boat, I just can't see a way to generate enough force to counter the suction with a kayak or even two.