When you do a kickstart install and have a auth --nisdomain DOMAIN --nisserver x.x.x.x the NISDOMAIN entry in /etc/sysconfig/network isn't written. /etc/yp.conf seems to be ok though.
hmmm ... it worked for me with the following line in my ks file: auth --enablenis --nisdomain baz.foobar.com --nisserver 1.2.3.4 --useshadow does that work in your case...?