Although I am not aware of any military or civil operator that screens potential pilots for their reaction to reduced oxygen levels
During my training in the Air Force we had several visits to the decompression chamber to practice this, the first time was during medical screening in the Belgian Air Force. I've had some more visits during my training in the USAF where we even did a rapid decompression exercise.
We noticed that not one of us was immune to hypoxia
Expanding gas in the intestins did his work too.
Bart