Yes. Absolutely. (But it's still not as expensive as alpha testing.)
From the OpenGL ES Programming Guide (for non-3GS PowerVR SGX) :
Another advantage of deferred rendering is that it allows the GPU to remove the hidden surface before fragments are processed. Pixels that are not visible are discarded without fetching textures or performing fragment processing, reducing the calculations that the GPU must perform to render the scene. To get the most out of this feature, you should try as much of the scene with the opaque content as possible, and mix, alpha test and abandon the instruction in the GLSL shaders. Since the hardware is hidden surface removal, it is not necessary for your application to sort its geometry from front to back.