This is not supported in 2.0. The problem is the embedded data in the snmp packets. When RME sends a tftp request to one of the devices on the DMZ the it will have the internal address embedded in the packet and will not be able to send the config back to the server.
You could try having RME only use telnet then open up the telnet ports for the server but really this is not supported in 2.0
LMS 2.1 does support this and was just released this month...
regards
phil