Talked to DD the CM yesterday. She said they can restrict access to the Club/Lab in EXTREME situations. The normal procedure would be to contact the parents, explain the problems and get the parents to help resolve the problem. Only in EXTREME cases is a child forbidden to come to the Club/Lab and that is done to protect the other children. She said what usually happens is that a parent is contacted and told their child needs to spend the rest of that day with the parents and return to the Club/Lab the next day. Even this doesn't happen very often.
That being said, I know there are some parents that refuse to believe that little Johnny or Suzie isn't a perfect angel when in fact the kids are horrible. I'm actually glad for the kids who behave that Disney has a provision to protect them from those very few who refuse to "play nice".
I forgot to ask her specifically about biters/hitters but she's worked with kids in Summer Camps for 4 years, and supervised a basketball league at our church for over 120 kids so she's experienced with "redirecting" the attention of kids who are unruly. The job requirements for the counselors are a college degree in a related field and 2 years experience working with GROUPS of kids so I'm sure the other counselors have as much experience as she does, if not more. I would be as comfortable leaving my child with them as I would letting them participate in any other group activity.
As with several other situations posted on the boards, if you have any special concerns, feel free to talk to the counselors when you board the ship. They really do want your child to enjoy the cruise.
Hope this helps.