I will state my bias from the start. I would avoid using the custom name. You are best off using the qualified domain name for your BIM Server. That is, the machine name given by the network along with the domain of the company. Something like: BIMServer1.mycompany.com.
When joining a BIM Server that is using a custom name there will be two parts to the BIM Server's name
Custom_name [ IPaddress_or_Domainname]
The value in the brackets is what is being used. The custom name is strictly for fun. This is important when linking with BIM Server libraries. If a BIM Server library was shared with Custom_name [ IPaddress_1 ] and another user joins with Custom_name [ IPaddress_2_ ] the other user more than likely will not see the libraries. This is most common when one user is outside the local network of the BIM Server and is using a public IP_address to connect.
To avoid all possibilities for problems, always use the qualified domain name and name conflicts will be avoided. Likewise, this also insures the proper network route will be chosen.
Graphisoft Technical Support