MHW's are performing duties of LNA's re: vitals, O2 set up, patient cares...but are not licensed to do so...
You are obviously in one of the very few states that has LNAs (licensed nursing assistants). Let me guess, New Hampshire?
The vast majority of the states have CNAs or STNAs, which are essentially unlicensed nurse aides. They are not licensed to do anything, as they do not have any licensure in the first place. They are, however, certified to perform basic patient care. Psych hospitals prefer to hire unlicensed mental health workers because their scope of practice is not restricted by a certification, and these people are working under the nurses' licensure.