If you use Active Directory
If WhatsUp Gold and all the devices to which you want to deploy the Agent are in the same domain, you are not likely encounter any issues since the default common name should be correct for your environment and DNS is able to resolve the FQDN of the WhatsUp Gold server.
If you do not use Active Directory or if you have a mixed environment
If systems where the Agent will be deployed may or may not be able to resolve the host name specified in the Common Name of the certificate, they will have to do additional planning to ensure a successful rollout. In this scenario, users must consider what DNS servers may require changes so all deployed devices can resolve the host name. Adding an entry into the HOSTS file on those systems is a workaround that can be employed.
Example Use Case
The administrator may want to monitor logs on devices which are not always on the corporate network (e.g., laptops). When this is the case, they must decide if they want to open ports on their firewall to allow connections from the internet to reach their WhatsUp Gold server. This scenario would also require the host name used for the Common Name of the certificates be resolvable both on the internal corporate network and the public internet.
Note: There is no single solution which works for all users in regards to what a WhatsUp Gold administrator should or should not use for the Common name (FQDN) field because the entry depends on the specific devices the administrator wants to monitor and their unique network topology/environment.