Except with respect to faculty members or lecturers employed on one or more campuses of the University of Hawaii who hold multiple part-time appointments or positions, in such capacities, any of which may be less than one-half of a full-time equivalent but all of which, when added together, aggregate to at least one-half of a full-time equivalent position, the board may deny membership to any class of part-time employees or persons engaged in temporary employment of three months or less; provided that no officer or employee entering service after January 1, 1928, who is entitled to become a member of any pension system under part III shall be entitled to become a member of the system.