As a former Court Appointed Special Advocate for children of juvenile court, my first question is: Did the advocate know the mother (in some other capacity) prior to the case-matching? If so, it is clearly a conflict of interest.
Second, my concern is that this person has biased him/herself against the father, based on what the mother may have said. Part of his/her job is to interview all parties involved with the child(ren), and to make a recommendation to the Court.
It sounds like conflict of interest -- not to mention biased and unethical. I would suggest voicing your concern -- preferably to your own attorney, as in PA, juvenile court judges put a lot of stock in court appointed advocates. Further investigation of this would be a good idea. You might want to call the director of the Court Appointed Advocate program to find out if there is a reason why they're not talking to the father. Good luck.