Not really quite a few. If you look at the number of performers on that page compared to the total number of working jazz musicians, it's a completely insignifi

Not really quite a few. If you look at the number of performers on that page compared to the total number of working jazz musicians, it's a completely insignificant percentage. I have never met a working jazz musician who didn't read music, or, more fundamentally, didn't have an incredibly solid understanding of western music theory.