Learning Modern 3D Graphics Programming with OpenGL 3
arcsynthesis.org
arcsynthesis.org
As you learn things, just check the reference to make sure GLES2 supports them: http://www.khronos.org/opengles/sdk/docs/man/
If you're stuck with GLES1.x then the book is useless to you.
I think if you learn OpenGL 3.3 (as in this tutorial), you'll get enough of the common stuff down that you can fill in the missing spots from OpenCL reference material directly.
Being experienced with OpenGL (or Direct3D, or game console) shaders will probably help for performance tweaking as the mindset is similar (memory access is evil, irregular memory access more so), but other than that I doubt it will help.