In OpenGL, the typical way that I've seen to set up a skybox using cubemapping is to create a cube in camera space, prepare a cubemap sampler with the appropriate six-sided texture, and then in the pixel shader use the camera space direction of the pixel as the input to texCUBE. What I'm wondering is, if instead of this, I set up the same cube, but then simply textured each face of the cube with the appropriate face of the cubemap texture, and then rendered the cube with a standard shader, would it achieve the same visual effect?
The only difference you would have is that you are doing texture lookup based on UV instead of direction.
This would mean that each cube vertex would need a uv or you would need a routine to calculate the appropriate uv based on the view direction ... which is basically us back at using texCUBE, with the exception that texCUBE is probably going to be more efficient that anything added as a function in the shader.
So, yes that would be the same in look, and probably about the same in actual performance, but texCUBE will likely always be slightly faster.
I did this once with a textured sphere - because I happened to have a textured sphere already, obviously drawing a sphere is slower than drawing a cube because there are more vertices.