Fortigate as DNS Server/Microsoft clients not communicating with Domain

I have a hub and spoke configuration over VPNs with my AD server at the Hub.  I setup my dns servers on the Gates following this information:

https://kb.fortinet.com/kb/viewContent.do?externalId=FD36649

I have the 5.6.3 OS at both ends.  The Gate will receive the zone without issue.  I can see the objects that i need to hit.  the Gate does DHCP on the internal interface and DNS is set to interface ip.  When the Windows machines login, it appears they are logging in with cached credentials.  When mapped drives are attempted, it prompts for user/pass.  when this is entered, they map.  If i change the dns to point to the AD server across the VPN instead of the Gate's interface, the machine logs in and the drives map as normal.  Am i missing some setting on the DNS server to work with Active Directory?  

Thanks,

Chris