No, if you are using your dns servers ns1/ns2.yourdomain.com then you do not need to use ns1/ns2.theplanet.com or use Orbit to update the DNS entry.
Pstar was asking if it is possible to create the dns servers on the machine and yet host the site using theplanet dns. If that is the case, it is possible. But if you want to move totally away from theplanet dns then you do not need to inform them about anything.
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are you saying i need to effectively point ns1/ns2.mydomain.com to ns1/ns2.theplanet.com?
Nope. You can run your DNS servers independently from theplanet.
If everything runs off your server then the DNS would also be controlled from the server which means yes, it would be automated.
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just say there is another option where i use my own nameservers and everything is automated, and i change over from ns1/ns2.theplanet.com
to ns1/ns2.mydomain.com - is there a chance i could screw everything up and everyones site goes down?
Well, if the ns1/ns2.mydomain.com is not done properly, the switch over to them might cause problems. But if you ensure that everything works then the switch over would be painless. If there is no change in IP addresses, you probably wouldn't sense any downtime.
It is like prior to propagation, all sites would be using ns1/ns2.theplanet.com then when the dns entry get propagate to that isp, it would do the seamless switch over to the new dns.
Usually what I do is to change a single non-active site over from one dns server to another then check to see if the site is still reachable within 48 hours. If it still works then I'll do the massive change. But make sure you check every entry in the DNS servers to be sure you got it right.