There's no inherent problem with Hempys IF you study the technique BEFORE setting up the grow and follow instructions perfectly. As Killa says, the medium is perlite/vermiculite. One of the things the Hempy style depends on is the pore size in the medium; soil has insufficient pore size. You can't do a flood-n-drain with dirt, either...
I guess I should re-phrase my earlier comment, lol... don't try any sort of unusual method until you know HOW it is different from a pot of dirt and WHY it can actually work.