Your servers's hostname is not in any DNS setup that your client host can see. Either configure it in your local DNS, which may take cooperation with whoever owns the domain, or put the entry in /etc/hosts on all these machines.
I published some time back a useful cookbook for just such setups, at https://github.com/nkadel-skyhook/nkadel-chef-hosts . It has good rules about if, and when, to set the hostname for "127.0.0.1" or fot the hosts local IP address. And it works well from "chef-zeo", if you want to avoid having to actually set up a server and just use git ocnfigurations.