The Hyuga class would probably need a coat of Thermion or something similar (like USS Wasp and QEC) but not because of the IPP heat. This may have been a concern early on, but the programme is well past the point of worrying about the IPP melting its way through metal.
The bigger issue would be the frames under the steel deck to support the weight and repeated force of the landing of a V-22/F-35B. The ship designers will be doing the maths and it may limit the number of landing spots and/or parking spots. This is no different to Ospreys landing on Ark Royal/Invincible/Illustrious, you just have to work round it.