I would prefer to have access from my local vlan and wireless vlan to the servers.
But didn’t want to all dns traffic into the VM’s (and depend on a testing environment)

Basically I want host resolution, and being able to utilizing the domain services in the testing environment, without interruption of my other services.

This is the solution in went for was using Conditional Forwarders

First the Hyper-V host:

I Installed the DNS Server role within Windows Server 2016.
Setup forwarders to google dns:

After that i will add the Conditional Forwards for my testing domain
I  in my previous post I created 2 Domain controllers, both hosting DNS.

I will then add my Hyper-V hosts IP to the DNS server of my router/dhcp on the needed vlans.
When clients send requests for the testing domain, they will get forwarded to the Hyper-V guests (DCs) and all other requests will go to the Google DNS (8.8.8.8, 8.8.4.4) – more info: Getting started with Google Public DNS

I did want a backup as well, so I installed Synology DNS on my Synology DS1511+
Synology DNS supports forwarding zones, with up to 2 forwarders per zone.
That’s perfect for my setup, added the 2 Hyper-V guest DC’s.
The Synology DNS would of course also need Resolution services enabled, so we can forward requests to the Google DNS (8.8.8.8, 8.8.4.4)

Then I will go ahead an update the DNS servers handed out by my DHCP on my normal client network and wireless clients.
This configuration offers failover/backup, because both the Hyper-V hosts and the Synology will be able to handle DNS requests and forwarding.