Does anyone know what YAST2 is looking for when it does it's ntp server search ?

I have a server ("ntp0" for the sake of arguments) that I have configured to run NTP and get it's time from - works great. Now I would like to sync all my other servers to ntp0. But when I have yast2 run a search for ntp servers it doesn't find it but if I put in ntp0 in the address field and run test it works just fine. Just wondering what I can do to make the ntp server search find ntp0. Might want to use it for other systems or appliances.