I'm not using my own NS's using SM's, so my question is can I delete the zone for "servername.servermatrix.com" or does cpanel still need it?

Ian

servername.servermatrix.com? It should be servername.yourdomain.com. And I believe the server will need that.. at least the 'A' record in that zone. If you don't have it, cpanel will warn you to add it back anyway. Believe it or not, your server will still likely need DNS type records to know where everything is located even if your actual DNS server is elsewhere.