“Is it legal for a parole officer to release the name of the person calling to report a violation of one of their clients?”

Parole officers have pretty wide latitude in looking after their charges, and I’m not aware of a legal restriction on divulging the name of an informant. But it’s a very bad career move for a parole officer to burn those who are helping him do his job and I’d be surprised if most parole officers did it on a regular basis. If you’re truly afraid, however, you may want to attempt to report the violation anonymously: send a letter or a fax without providing your name, or call from a payphone and refuse to give your name. Unfortunately the facts and circumstances of the information may be such that there’s no way to hide your identity, in which case there may not be much that the parole officer can do. In addition, if the parole violation is severe enough, you may be needed to testify in a hearing on the parole violation, in which case the defendant has a constitutional right to confront their accuser.