Setup seems to push me to use an external dynamic IP address service.
Setup assumes a dynamic IP I think because it's assumed you are setting up your Ubuntu Server on an existing LAN with a working Internet connection, as an installation configuration and nothing more. While I also have static IPs, I find the Ubuntu setup default convenient. (That all changes of course if you have no existing LAN.)
In any case, once the machine is running, you have the option of setting an external interface to a static IP. That option is available during Zentyal's initial configuration as well as being a configurable item later.