This is the good thing about adhering to the standards - there are always provisions to accomplish what you want to accomplish, whereas ignoring the standard often leads to unresolvable conflicts.

You said your AIX systems are immobile anyways, so you probably want to get them always the same IP address anyways. You can do so at the DHCP servers configuration by reserving a fixed IP for the AIX system. You could move this IP at the top or bottom of the DHCP-served address range and exclude it from that range accordingly. Don't use the DDNS means you probably use for name resolution of DHCP-based systems but reflect the quasi-static IP address with a static DNS entry. This way you get name resolution even if the system is shut down.

I hope this helps.

bakunin