On progression server at least on Phinigel, Cheif RokGus spawn at his original location in the Temple of Droga position#8 (Ledge Room).
Here's a link of the map & original spawn location for those who don't remember or don't know the place:
Map Temple of Droga
So those who seek information about him on Phinigel take my words he spawn there, I killed him last night.
October 2nd, 2016
Edited, Oct 3rd 2016 11:32am by Dranem1974