How about the RedHat Client?
I am having the same issue, I have a SUSE 9 ddns setup, and have a RedHat machine that will not register with ddns. All other cients in the network register (windows, other redhat clients, etc.), but not this one redhat machine.
the redhat box does get it's IP and all other network setting properly from the suse server (including dns server info), but it will not show up in bind.
did you get yours fixed or did I interpret your post incorrectly?