Desktop Central Server applied in DMZ

Hi Community,

my environment forces me to deploy Desktop Central Server inside DMZ. We also have a Workgroup and Windows 7 Home Premium Clients.
DMZ is realised with an Asus Router rt-ac68u with tomato firmware.

Desktop Central Server is connected via VPN to local LAN but the system is not able to auto discover the systems.
Next to the missing auto discovery I cannot share files through a shared folder. (HTTP file sharing works)
I also cannot deploy IP printer (I guess this is because of the not working file share)

Is Desktop Central able to work with an VPN connection?
Or do I have to configure any special settings?

I have tested it shortly in local LAN and havent discovered problems.

Thank you very much