You probably can't just add the .3.1 address to the server as the server doesn't sit on the same physical network segment as the rest of the .3.0/24 subnet (which I suspect exists soley within the sonicwall box).

Can you ping from a .3.x address to any .2.x address (not just the server) and get a reply? Vice versa? Does the firewall have any log files showing what it's doing with the packets? Do you have any sort of sniffer to see if any .3.0 packets are entering the .2.0 subnet?

-jk