Ok, so this is a sub-optimal solution. Perhaps it will give someone a better idea. It's single positive aspect is that it works. From an elegance perspective it sucks. In private correspondence, it was suggested that turning off console is a bad idea. That notion is agreeable. One certain bug is that, if the user switches to ttyE0 and runs /etc/rc.d/xdm stop he gets logged out.
--------/etc/rc.d/xdm---------------
#!/bin/sh
#
# $NetBSD:
xdm.in,v 1.1 2008/12/05 18:55:22 cube Exp $
#
# PROVIDE: xdm
# REQUIRE: DAEMON LOGIN wscons
# KEYWORD: shutdown
$_rc_subr_loaded . /etc/rc.subr
name="xdm"
rcvar=$name
command="/usr/X11R7/bin/${name}"
start_precmd="xdm_prestart"
stop_postcmd="xdm_poststop"
pidfile="/var/run/${name}.pid"
required_files="/etc/X11/xdm/xdm-config"
extra_commands="reload"
xdm_prestart()
{
local ttyE0_on='/^ttyE0/ s/off /on /'
local console_off='/^console/ s/on /off /'
local sed_cmd="$console_off;$ttyE0_on"
sed -i -e "$sed_cmd" /etc/ttys
kill -HUP 1
return 0
}
xdm_poststop()
{
local ttyE0_off='/^ttyE0/ s/on /off /'
local console_on='/^console/ s/off /on /'
local sed_cmd="$console_on;$ttyE0_off"
sed -i -e "$sed_cmd" /etc/ttys
kill -HUP 1
return 0
}
load_rc_config $name
run_rc_command "$1"