In any proceeding before the division, any person may be represented by an attorney at law admitted to practice before the highest court of any state or territory of the United States, or the Court of Appeals or the District Court of the United States, or for the District of Columbia. Any individual may, however, appear before the division in his own behalf, an authorized member of a partnership may represent the partnership, and an authorized officer of a corporation, trust or association may represent such corporation, trust or association, however no such officer may participate in an adjudicative proceeding as defined in RCW 34.05.010 unless such officer is also an attorney at law.