Hi…
What is more to say …!!:?.. 
The title had said everything…
AFAIK beast is a raytrace render which is traditionally run like most raytrace renderers on the processor.
For a little general article that covers raytracing please take a look at http://www.codinghorror.com/blog/2008/03/real-time-raytracing.html and any sublinks of interest.
In theory it would be possible if the unity team rewrote beast’s code to be executed on GPU’s, i have no experience in the limitations, but i can imagine the differences between cpu- and gpu architectures is one thing that could cause many technical issues.
However i should clearly note that raytrace rendering is still making only it’s baby steps on consumer-level GPU’s.
NVIDIA’s Optimus (GPU Rendering Solutions for 3D Designers | NVIDIA) Is a quite recently released C-library that can offer such possibility.
V-ray has been an esteemed gpu-render technique (mainly employed in 3ds max) for a little while now.
But here is a quite detailed article, also comparing against Optimus: rodlima.net - rodlima Resources and Information.
I think the last link illustrates quite clearly how things can differ in both directions, it explains the difference between “traditional” raytracing on a cpu and how a gpu normally handles it’s renders.
Likely the resulting performance gain is just too small to try and incorporate such a big change in the beast renderer which could add many inpredictabilities/bugs at the same time.
However… If unity would be able to incorporate Optix/RTGPU/OpenRT , it would certainly be interesting to toy with atleast!
Blender has GPU rendering as well:
http://wiki.blender.org/index.php/Doc:2.6/Manual/Render/Cycles/GPU_Rendering