Latest fglrx drivers has a new compile flag: --NoXServer From the fglrx manual: GPUs can be used only for computation purposes (commonly seen with AMD server graphics products or headless GPUs) where X Server is running on non-AMD GPUs or in cases where there is no X Server running on the system. AMD provides support for headless implementations of server GPUs. [http://www2.ati.com/relnotes/amd-catalyst-graphics-driver-installer-notes-for-linux-operating-systems.pdf] It would be nice if a new USE can install the fglrx driver without the xorg dependency. The flag --NoXServer seem to work from 15.7 version. Thanks.
x11-drivers/ati-drivers has been removed, per bug 582406.