Yes, you have to use WCCP to redirect the traffic to the Ironport. It would look something like this:
access-list ironport-wccp extended permit ip host X.X.X.X any
X.X.X.X is the IP address of your Ironport appliance. If you have more then one, just add the same ACL with it's IP address listed.
wccp web-cache group-list ironport-wccp
wccp interface INT-NAME web-cache redirect in
These two commands will direct the traffic to the WSA. INT-NAME is the name of the interface on the ASA that you want web traffic redirected on.
After you get this configured, try to browse to the web on the wireless network. Then do a show wccp from the ASA and you should see packets being directed to the Ironport.