They do loot them ofcourse but last time i hunted them, just few days back VII and VIII were the comps the looted the least by far. But this does change often.
So far, that's been my experience. Got 2 tier VII from a L16 Motorhead, moved on to the L33-39 ones and only got Tier I, II and III. I'll keep going for a couple more days, but I need 129 more and I suspect it's going to be a long grind.
Primordial Longu mid matturity and up. Not sure if the small can give you any, never got some from young so switched after first 2 hunts to the medium one near Proteron.
But well they are pretty rare, did the whole iron mission and looted maybe 30-40 of them. Had days without any in loot!
I'm certain Phasm's do
I'll try that next time I'm on Calypso.