haku's so called "ultimate" jutsu wasn't all that ultimate....if u watch the eps, he says "i can't keep this up much longer. this jutsu requires alot of chakra" or somethign like that.......so if the user can outlast his jutsu, then they win. granted shika probably doesn't have enuff stamina (or is even willing) to outlast.....but someone like naruto or sasuke (as they are now) could certainly defeat haku.....