I brought a symmetrical character into CC4 as a “prop” (as shown in a Reallusion tutorial) and used AccuRig with “forced symmetry” to create a rig for it. It now shows type “humanoid” and everything looks and works fine.
I did not rename any bones but for some reason I still can’t activate any of the symmetry functions, for example in “Adjust Bones”, where I wanted to fine tune the facial bones just now.
Anybody have any idea what’s going on?
Aside from the fact that symmetry function is not supported for Humanoids (which it should IMO), Adjust bones does not work right either: Adjust Bones does not work right for Humanoids - Feedback Tracker
That is disappointing indeed…especially since the rig was created inside CC using AccuRig, I wonder what the problem is. 
So what types do support symmetry? Is there some workflow I can use with a custom mesh to get symmetry in CC?
Only Standard CC characters support symmetry. I use Blender for Humanoids. Mesh with Snap to Symmetry (this is non-destructive method compare to Symmetrize). There is also method for Bones but I do not remember exact workflow in Blender, you need to google it.