I'm not sure if it will help, but there are some dns settings in the settings, NTA settings section. The one that you refer to only governs node management (not endpoints) to the best of my knowledge
1. if your DNS servers don't have internet connectivity remove the root server list from them so they don't know how to resolve addresses outside their domain.
[these are not servers of last resort, they are the root name servers.]
Your servers should immediately return NXdomain and will improve performance.
2. If these DNS servers don't have access to any other DNS servers then disable recursion on them; they will not then try to contact other DNS servers to answer queries on behalf of clients.
3. assuming you've windows firewall enabled block port 53 TCP and UDP outbound from those servers to IP addresses not on your network
this is an ugly hack that will cause delays in DNS resolution, but no worse than you already have.
You might do this anyway as it prevents breakage should someone re-add the root hints or re-enable recursion.
I think you hit the nail on the head.
There were two issues:
1. Solarwinds queries the HECK out of DNS especially with IPAM, Netflow running.
2. Being that this is a closed network, the Root Hints file had the DNS servers was sending queries out to Japan (or wherever outside the local network).
Removing the servers from the root hints file is the answer here.