Is there anything that needs to be done in a WHM/CPanel setup in order to allow customers to register nameservers to your DNS server IP addresses?

To get it to work you should just setup the customer's name servers with two IPs that resolve to the server you are running. And of course make sure the customer set the name servers up wit hthe domain registar :)

Great, that's what I thought I had to do. Thanks for the info!