I'm pretty sure that military pilots have to go unpressurized to 25,000 feet in order to be qualified. however they don't have to stay there for very long. and certainly not as long as the duration of a commercial flight.
When I did my training (Canadian Air Force, in the early 90's), we only had to go through controlled hypoxia training that allowed us to experience high altitude sickness, and therefore (hopefully) recognize the symptoms of it so we could react to some failure at altitude.
We basically had to do menial tasks, like read a deck of cards, play "paddy-cake", etc., and then put our oxygen masks back on once we thought we were too impaired, while a technician was there with us.
However, I think the simulated altitude was 20k or 25k feet.
Needless to say there's a reason that O2 is (legally) required in unpressurized aircraft for anything over 10k feet.
Here in the US oxygen is required for the primary crew at over 14k cabin altitude. At 12.5-14k it's required after 30 minutes. No requirement under 12.5k.
I have flown at 12k for 1 hour and could tell that the air was much thinner and that going much higher would have started to impair.
I think that most commercial aircraft run somewhere between a 6k and 8k cabin altitude and as such a whole different set of rules apply. I don't know for sure - I'm only a private pilot.
