Human bites can carry very dangerous bacteria and germs. They should be taken seriously by the daycare, and I agree with you that children who cannot be cured of the habit of biting others should be forced to leave the daycare.
My nephew, as I mentioned earlier, was a biter. My dear sis worked diligently with him to solve the behavior, but NOTHING helped. One day BIL came home from work, found out Nephew had bitten someone again, and BIL lost it. He grabbed Nephew, bit the crap out of his arm and informed him that Dear Old Daddy would be biting him for each and every time he heard of another instance. My nephew was under two years old at the time, and I cried buckets of tears because the "poor little baby won't understand why his daddy bit the crap out of him! He's surely so confused and upset!" But you know what? He NEVER bit again.
Can't say I recommend this approach, but it worked for the one compulsive biter I've known.