You will rarely hear a dim chord being played by itself, let alone the vii pure dim chord because the dim7 (or the V) sounds so much better and fuller. I use it every now and then, but there are other things that sound better than the natural chord that is formed there.
Just like on the ii or iii, you use the m7 chords instead of the natural minor chords that are formed on them because you want a different sound. Not saying that it's being ignored or not mentioned, just saying there are other choices you can use that work better for the sound you want to achieve.
As long as you know the theory behind these scale degree chords, you're free to choose other chords to play. Some people don't know any better, some were taught wrong, others don't even care. It's very important to get the correct teaching early.