TCP Wrappers is useless in this case, because I doubt Oracle is compiled with libwrap support.
You need to troubleshoot why iptables isn't working correctly. check /var/log/messages, dmesg, any output when you try to start it...
The previous sysadmin didn't harden the system. If you can't get iptables to run, something is broken, not hardened.
Can you not just talk to the windows admin and have him figure out what is trying to use oracle on your cluster and have him disable it?