I've never heard of that one, although I do know people who use Preparation H to minimize the bags under their eyes!!
The ingredients in Prep H don't seem to suggest anything that could stimulate hair growth. Here they are:
Active Ingredients: Preparation H is available in ointment, cream, gel, and suppository product forms. The Ointment contains Petrolatum 71.9%, Mineral Oil 14%, Shark Liver Oil 3% and Phenylephrine HCl 0.25%.
Shark liver oil does contain some healing properties so maybe that's what stimulates hair growth. Here's a bit about shark liver oil:
Also with the petrolatum and mineral oil in Prep H, I'm sure there are other things that can improve hair growth that don't contain these pore-clogging ingredients. If it's really the shark liver oil that helps the hair and scalp, maybe you should invesigate that for hair growth?