The Server Density UI tries to save space and reduce clutter so it will only show the hostname of a server on the server list if the hostname is different from the name you have entered into Server Density. The agent will automatically set the hostname of the server when it posts back.
If you call the server "MacBook Pro" but the hostname is "Steves-MacBook-Pro.local" then the hostname will be shown in the server list. But if the hostname and name match, the hostname will be displayed separately.
You can edit the name of the server by clicking the cog icon in the far right, then clicking edit
Change the name of the server then click Save: