If you are configuring your system to use DNS for host resolution, AIX defaults to using DNS resolution before using /etc/hosts. CDE depends on the host name & IP address assigned to properly function, but during the login sequence, your system is querying the DNS server. To speed up the login sequence, and to let you resolve names in the host file prior to requesting them from DNS, create a file called /etc/netsvc.conf, and add this line:
hosts=local, bind
This will allow AIX to resolve your hostname for CDE and improve login time.