I use debian, and unfortunately don't have access to a Redhat system. On debian, the conf is in /etc/initramfs-tools.
if you have a full running system, then it sounds like it's nearly working. Check the mount points in your /etc/fstab on the netboot image,
as well as the permissions for any exports related to the image.
If you are getting errors at boot, please post them. Also, please post the fstab from the image as well as any nfs exports related to
the boot image.