You should ask this question in the OpenCL forum topic area.
As far as I know, AMD is still working on a fix for supporting GPGPU without an active X session. I know you can set things up such that an X session is started at bootup time, and configured such that when you ssh in, you can invoke OpenCL code. But I don't have the details on how that is done, I just have access to a cluster that lets me ssh in and use ATI/AMD GPUs for OpenCL. You might only have to set the COMPUTE environment variable in your shell (analogous to the DISPLAY environment variable).
replaced LightDM with GDM, amd followed this guide: http://developer.amd.com/support/KnowledgeBase/Lists/KnowledgeBase/DispForm.aspx?ID=19
Still as others have mentioned: It would be nice to be able to do this with out running a Xserver.