Haw. Code R. § 16-201-7
Upon timely motion and at the discretion of the authority or the hearings officer, the department or any person may be permitted to intervene and be admitted as a party in a proceeding before the authority or hearings officer if the department or that person has a substantial interest in the outcome of the proceeding which is not protected by the interests of any of the parties, or the intervention shall be conducive to effectuating the ends of justice and to achieving the goals and purposes of the authority; provided that no intervention shall be permitted if the intervention shall unduly delay the proceeding or harass, hinder, or prejudice the rights of any party to the proceeding. The complainant in a disciplinary case, however, shall not be permitted to intervene or be admitted as a party.
Haw. Code R. § 16-201-7