In-Band Virtual Gateway is the recommended configuration. What you have in the link is In-Band Real IP. You can use either one... with real ip you will need static routes. In IN-Band virtual gateway, the NAC will bridge the traffic from the untrusted to the trusted.
Basically the ssid is mapped to a vlan like 50 and that is passed onto a dot1q trunk to the switch. Vlan 50 is not routed and the only other port on vlan 50 is the untrusted port on the CAS. The CAS then bridges that to... lets say vlan 51 which is routed on the network.
Every time I have to deploy one of these, it still confuses me somewhat... So hope this doesn't confuse you.