Thanks. I figured out the problem. The DHCP server on our end deals the IP addresses based on client mac address. Because the client mac was unknown the client was dumped into the "guest pool".
I've spent a few hours googling and I can't for the life of me figure out how to get the mac address for the tun0 interface (client has OS X).
I know this is a client-side issue now and not a server side one, but if someone has an idea it would be greatly appreciated.
ifconfig -v tun0
only returns
tun0: flags=8851<UP,POINTOPOINT,RUNNING,SIMPLEX,MULTICAST> mtu 1500
inet xxx.xxx.xxx.xxx --> xxx.xxx.xxx.xxx netmask 0x00000000
open (pid 80320)
and tun0 does not show up under interfaces in Network Preferences.