HH really only creates problems because the stats for some things are different, and you pay a premium in points for some things that aren't as important in 40k, which creates a huge issue if you try to comp it. If comp isn't even in the cards, there's no reason not to at least try it out, IMO. The only truly glaring thing in those books is that grav guns are completely different (read, ****ty in comparison) from C:SM ones.