Get rid of surfaceparm nodraw. This section:
Originally posted by Arkon11
surfaceSprites vertical 5 20 25 2000
blendFunc GL_SRC_ALPHA GL_ONE_MINUS_SRC_ALPHA
Is what maps a texture to the surface. (See the "map textures/..." line?) Try making yourself a jpeg that's all black and replacing the stage I highlighted with:
Then you should be able to apply the shader to a brush and just get grass sprites sprouting from an invisible surface.