Well, his loyalties lie more with the DH than the BoM, so he is technically considered a Hunter.
“Voporak is a time-sensitive servant of the Dark Hunters and a former clan leader on Stelt.”
“Voporak was once a member of Sidorak’s species and a clan leader on the island of Stelt. Seeking to usurp his position of power, Sidorak encouraged the Makuta of Stelt to select him for experimental mutation. By combining Energized Protodermis, Roodaka’s mutation Rhotuka, and other mutagenic substances, they transformed Voporak into a being sensitive to shifts in time, one that would be able to locate the Kanohi Vahi if it ever came into existence. The Makuta of Stelt lent this being to the Dark Hunters to learn discipline, but Voporak became loyal to the Hunters rather than the Brotherhood as a result.”
Taken from BIONICLEsector01