If you want to use pure udevfs then don’t set boot devfs on boot time in kernel config.
CONFIG_DEVFS_FS is not set
(in .config)
To use udevfs linux device naming convention install udevfs and do this step:
# emerge udev
Then
kernel /bzImage root=/dev/hda3 boot=nodevfs
(in grub.conf)
now when system boots it’ll use udevfs.