Use the XG Firewall as a DNS server over SSL VPN (No AD DS)

I've setup an SSL VPN for a client but I'm having a DNS issue. They are 95% Mac with a few Windows based PC's. They don't have Active Directory so no 'true' DNS servers are in place. I currently have the LAN using the XG as the DNS server with a few entries of necessary devices. They have a desktop that hosts Quickbooks and some files. They also have a NAS that hosts most of their data. I have DNS entries setup on the XG Firewall for those devices and it works just fine while on the LAN. However, I cannot get those device to resolve over the SSL VPN. Not sure if it can't be done or if my configuration is incorrect.

Can anyone point in the right direction?

Below is my configuration and firewall rule: