I just committed Cg support for ES 2.x render system.
NVIDIA doesn't provide it's Cg parser source code (at least not a usable one), so a Cg to glsl converter is used to do the trick.
You can download it from: http://code.google.com/p/hlsl2glslfork/
I added a new CMake flag named "OGRE_CG_SUPPORT_FOR_GLES2" that is available if you have the ES 2.x render system.
The code needed for this support on the OGRE side is finished as far as I can tell.The converter doesn't do such a good job in many cases, I fixed some of them in this patch - there is still some work on it to get it to be prefect.
- edit - they committed my changes.
Unity3D uses the same parser so it has the same or worse Cg support for ES 2.x.
All the code is committed to the trunk.