Could you please consider re-reading the following section of the WinGate help file, to configure your 2 AD DNS Servers in the way we recommend?
WinGate 6.2.1 help file --> WinGate Security model --> WinGate in an Active Directory --> WinGate in an Active Directory
Basically, your LAN Clients (including the WinGate server LAN Client) will have the AD DNS Servers set on their network cards pointing towards the LAN.
The AD DNS Servers will be set to forward to WinGate’s DNS server.
WinGate will be setup to never send the DNS query received by the AD DNS Server, back to the AD DNS Servers (to avoid looping), it will send it on to an upstream DNS Server on your External network card. Putting the AD DNS Server into the Advanced Options in WinGate will avoid the looping.
(Windows) Start menu --> Programs --> WinGate --> Advanced Options --> DNS.
Putting the lan side DNS in wingate can became a security breach???
--> My understanding of this post is that you want WinGate to handle the internet DNS requests. So forcing the WinGate application to use the AD DNS Server for internet DNS lookups is not your desired result as far as I am concerned, and hence this question is irrelevant i.e. I do not have time to research that scenario.