At the hearing all persons interested are entitled to be heard and may present testimony either oral or written. All witnesses shall be sworn, and a transcript of the proceedings shall be kept by a stenographic reporter. All the provisions of this chapter in reference to the subpoenaing of witnesses and the taking of depositions are applicable to the hearing before the supervisor. On the request of the supervisor, a hearing officer in the Office of Administrative Hearings may assist and rule upon legal matters, but such officer shall not make the determination specified in Section 3306.