Hello,
we are using NAC with MAC authentication.
Known MAC address are in End Systems group and our rules "move" the devices into a VLAN and the device get access.
The rules looks like "if the MAC address of the device is in a End System Group and the authentication type is MAC then use the accept policy ...".
If no rules match the last rule is the catch-all rule that will collect all unknown devices.
And our catch-all rule will put all devices in our guest vlan. But in your case I would change it that all unknown MAC address will deny.
So you don't need to deny special address and catch-all unknown devices.
I hope this will help you,
Axel