If that doesn't work, I have quite a few different setups with NAT and hubs and robots on different subnets, w/ or w/o tunnels, etc...
Search for robotip_alias also, I'm using that with a robot behind a NAT.
If not, I'll need a little more visual and/or routing and IP info to try to see what you are doing to see if I have something setup like that already working.
Running Server 4.0 and associated program versions.