Hello,
Is it the same remote DNS provider for all domain names on the server? If so, instead of enabling "Allow Remote Domains" in "WHM >> Tweak Settings, you can add the IP addresses of the remote name servers to the following interface:
"WHM >> IP Functions >> Configure Remote Service IPs >> Remote Name Server IPs"
Users are permitted to add addon or parked domains only with nameserver IPs in this list.
Thank you.