Honestly it’s grammatically a little hard for me to understand that phrase, (English is my second language). But here are some info regarding the veg.
Painted veg are clustered and called using these clusters. So basically it makes one call for the cluster and a bunch of veg appear by that one call. As you are far away clusters are large and as you get closer clusters get smaller. So we can have millions of vegs (as it is +15 mil in kite level).
You can also watch this twitch when you have time (from minute 56 the technical talk starts, and from 1:40 it’s specifically about terrain and veg) to get a lot of info regarding the improvements.
I felt like asking you to watch it because you mentioned you are busy and not much active lately on UE4. If you have already watched that, then I’m sorry for the wall of text. 
Also for the black screen issue when you was loading the kite demo level here is how it should be loaded:
Hope that helps.