Hey there! If you wanted to block all UDP traffic, you would change the UDP_IN and UDP_OUT sections to have no IPs, so they would look like this:
# Allow incoming UDP ports
UDP_IN = ""
This would keep DNS from working on the machine.
Firewalls are not domain-based, so there isn't a way to stop that type of traffic for just one domain. This would affect the entire server.
Since network connections are typically pointed at an IP address, I wouldn't expect there to be a need to filter UDP traffic based on a domain, as there isn't a service that's listening for domain-based connections based on UDP.