Though I do not agree with hitting a child, they do need to start the process of disipline without being slapped, hit or whatever. Espically with a child that is hitting, hitting them will only confuse them if you tell them No Hitting and then mom or dad turns around and hits the child, know what I mean?
My daughter bites, she is 15 months old. She thinks it is a game and when I tell her "No Biting, that hurts Mommy (or Daddy)" she will laugh and try it again. I do attempt to dirvert her attention to something else, and sometimes it works, others it does not.
We are also starting time outs/corner after she has been warned 3 times not to bite. I place her in the corner or another area without toys(well I have to make sure she stays there so I usually hold her there) for 1 min. She seems to understand she is in trouble (she crys and fusses while in the corner or placed in another spot) and afterwards will not go back to biting for awhile (and cuddles afterwards also). I also explain to her why she went into the corner and once again that biting hurts.
Hope this helps.