It occurred to me that Paulo Aukar wrote in gmane.os.netbsd.devel.pkgsrc.user:
> You maybe should insert the following string at 
> /usr/pkg/xorg/xdm/Xervers:
>
>:0 local /usr/pkg/xorg/bin/X  vt05 -nolisten tcp

Contrary to popular belief, this will not solve all xorg problems :(

The above line is really only needed to get xdm to play nice, IIRC.