As Mylon posted here
https://bitcointalk.org/index.php?PHPSESSID=vpar9ssp7nbh69ok8m81komgk4&topic=28402.msg2649626#msg2649626
I have the same setup running.
cgminer 3.3.1
I don't use any /etc/X11/xorg.conf file.
I do have a monitor connected to the AMD GPU, but do not use it if I am mining.
(waiting for my ASIC)
cgminer has no AMD GPU set/query
bfgminer DOES adjust the AMD GPU and report status
It can be done.
They seem to share a lot of code but obviously there are differences in the GPU portion.
If I do run X11 with the monitor on the AMD I take a hit on one CPU core, the system input gets laggy, and it mines less.
It does work as it is, and cranks out the hashes.
I'm not bitchin/requesting features, just adding my 0.0000002 LTC.
thx again for cgminer