Seems like they did in the last patch. starting yesterday the spawn rate of the required npc's went WAY up. All cept Maybe garreg stonecrusher in Wailing Caves.
But the other 4 seem spawn every 30min now, I found them all in one day, after 3 days of finding nothing before the patch.
TWo of them i even witnessed them respawn twice in under 30min. So why i think they may have fixed it.. cause it was so ridiculously difficult to find them. (with other players killing any named they see and such)