Because no one answered so far, I will add a few things, maybe it helps. This looks like mixed issues to me, best would be if you could attach a simplified scene which makes troubles using DR.
render nodes at random seemingly just can't find FP assets
ForestPro 5.x-part:
What assets are you refering to? Textures? Distribution bitmaps? Xref objects? What does the asset tracker tells you in a problematic scene? Are you aware of 'ATSOps.CheckNetworkPaths=true' which actually checks items with network paths in the asset tracker (not only telling you that it's on the network...)?
Using FPs own assets should always work if you have installed FP on all nodes because it adds its (local) paths to the external files list. Some assets (like distribution maps) have/use a path, others have none.
Additionally there are registry keys generated, pointing to distinct sources. Especially "HKEY_LOCAL_MACHINE\SOFTWARE\Itoo Software\Forest Pack Pro\TexturePaths.", see
Installation and customisation for a complete guide.
Using own library items/presets is another story but the rules are the same as for any other (not FP-) assets in a scene (with the advantage that you can xref your objects).
ForestPro 6.x-part:
But the real trouble starts with installing, upgrading to FP 6.x. The standard installation is fundamentally wrong when it comes to paths/userprofiles/library location and networked/multiuser environment. I wrote that also to iToo support in June, extract:
Btw: deployment of FPP 6.x was just a nightmare. What a bad decision to install the libs in a user directory (!?). I had literally to change EVERYTHING from the defaults (moving libs to a suitable location - NOT some user profile, copy back old 5.x libraries to because older projects linked them, customizing all paths explicitly in the registry and so on).[...]
This one helped me doing so and now it's running without any issues:
https://forum.itoosoft.com/faq/installing-forestpack-6-assets-in-a-shared-network-path/I'm frightened of touching the installer again, that's the reason I still not have upgraded to 6.1.2. :)
Good Luck