did you try set export DISPLAY=:0 in ssh?
Yep, no dice.
The only time xdpyinfo responds with anything is when DISPLAY=localhost:10.0 (it seems to default to that for ssh -X or ssh -Y).
This is the Xorg command that shows up with ps
/usr/bin/Xorg :0 -nr -verbose -auth /var/run/gdm/auth-for-gdm-gGzbGV/database -nolisten tcp vt1
so for all appearances, access control isn't being disabled, even though I followed the instructions for doing so. probably due to a failure of gdm-restart.
[root@radeonforce ~]# gdm-restart