No man he popped once, despawned and then I killed some PHs and he spawned again >< Just terrible luck, he despawneed after 6 hours though. Should be despawning again right about now so good luck!

Hate to necro this but I have had 3 brother Z's spawn in a row. I used to do this quest on live and you would have to wait approximately 40 minutes for him to walk the zone then he despawns. You can check this yourself on the progression server.