A few do, but most of them don't.
I think the ones that do you have to pay for with a credit card in advance.
Cinderella's Royal Table definitely has tip included, and I believe Hoop dee doo Musical Revue does as well.
I'm not exactly sure how they deal with this on the dining plan. We paid OOP for CRT in January, because I had extra meals planned anyways. If you're using the Dining Plan they have a special way that they handle it.