Checkboard, I agree that a positive touchdown will not prevent hydroplaning, (Re #15 “will effect aquaplaning after the landing”), but I suggest that it can reduce the risk of hydroplaning immediately after touchdown.
Another NASA reference, although not stating specifically that a positive touchdown will help, discusses several factors.
In particular, the evidence of tyres not spinning up at touchdown – infers that positive ground contact will aid the initial motion.
Similarly, well structured technical arguments are made by a respected researcher from a reputable organization to support this theme -
pages 7-9 in “Safety aspects of aircraft performance on wet and contaminated runways”.
In the section conclusion, there is a clear statement of the need to land positively:-
Therefore, it is normally advised to pilots to accomplish firm touchdowns when landing on wet and water/slush covered runways. This will improve wheel spin-up.
The risk of hydroplaning remains with the speed above the hydroplaning speed. The safest course of action would be to avoid known conditions, but for landings on wet and water/slush covered runways the risk of inadvertent hydroplaning/no or slow wheel spin up, can be minimize with a positive touchdown. I have yet to see evidence of any detrimental effects, but from the above, be it myth or truth; a positive landing contributes to landing safely.