Don't think the H8K has the performance/survivability to justify being perked. While not many were built, it was worked hard making those 170 far, far more significant to the war than, say, the Ta152 (less than 50), Wirbelwind (less than 50), Ostwind (less than 100), F4U-1C (200), C.205 (250), N1K2-J (just over 400) or P-47M (100). The PBY-5A was more significant, true, but that sort of relationship has not gotten things like the C.205 perked to protect the usage of the C.202 in the MA.
I am skeptical of perking anything that lacks the performance or survivability to justify perking it. That only leads people to almost never using it as it is a waste of perk points, see Ta152 and Spitfire Mk XIV as examples. People will use the PBY-5A if they want to just as some people use the P-40E because they want to.