What happens when someone doesn't like you and decides to DDoS your DNS servers?
Though if it's only your site on the DNS Servers, they might as well just DDoS your website.
Though if it's only your site on the DNS Servers, they might as well just DDoS your website.
Do both.
If they run additional business in hosting DNS, websites, email, and so on, as is common - that's really got nothing to do with the setup they need to act as a registrar.