UPDATE: I’ve discovered that it’s only the AU files that don’t show up properly in Renoise. I forgot I actually had VST disabled in Renoise, but when I turned it on, all the Arturia VST showed up as expected. So, this is less dire than I had imagined, but it’s still a bug / problem that Renoise isn’t seeing AU files for the Arturia Collection synths (anything past V2 for each synth, or anything added in V Collection 6).
This report is a bit redundant with the ‘arturia V collection 5’ post already made in here, but since that post didn’t receive any responses from the devs, and since Arturia has released a whole new update (V.6) of their software line, I felt I should make a new post about this ongoing issue.
Most Arturia plugins aren’t showing up in Renoise on my iMac (El Capitan).
Some much older Arturia plugins show up, but none of the recent additions (Buchla, DX7, CMI, etc) show up at all, and all the Version 3 updates of various plugins (Prophet V3, CS-80 VS, etc) don’t show up at all either. Essentially the past 2-3 years worth of their product updates don’t seem to show up in Renoise at all, either as VST or as AU.
They show up just fine in my other hosts (Ableton, Reason) so this is something specific to Renoise (and, possibly, Mac OSX).
Hopefully this can be fixed, as I’d rather like to use my SEM V inside Renoise one of these days 
-Michael