Hello there,
im trying to make an oldschool style inventory (where on a HUD, 3D objects spin) and I was looking into ways of going about drawing actors over the HUD for giggles. Its been a dead end for months now but then I found out about postrenderedactors. I got a little excited.
I set up an experiment: Draw a simple widget on the screen, In DrawHUD call DrawActorOverlays when the array is populated and see if the actor truely does get drawn over everything else
spoiler alert that didnt happen 
So my guess is postrenderedactors is some kind of debug tool?
I could always use render targets / scene captures for what im trying to do but im reallllllyyyy trying to do it the old fashion way of drawing straight to the screen