Your hostname is irrelevant to the domain names you host thru apache or whatever http server you use.
All computers are named, this is the hostname to associate a name with the machine with. Think of it like this, would it be easier for you to remember the machine by a number or a name?
By default, most machines in *nix environments are named localhost and have a domain localdomain until you decide to name it how you like.
You don't need to add your two domains to your /etc/hosts, I'm sure you'll be setting up DNS with Bind or the like to resolve name resolution for such domains.