The registry probably has rules on what they can do to customers that curtail them; they are probably not bound (ha!) to anything wrt serving DNS requests.
I'm saying why would you let a CDN be your registrar in what sounds like an abnormal registrar agreement. (If they block you from the CDN, what happens then?)
I believe the path for Krebs when under DDOS was free CF cloud to akamai to special status (from Google?) Using CF domains with or without CF's normal services turned on would have made akamai impossible until a transfer process to a real registrar completed leading to an extra week or so of downtime.
