Thank you.
My exposure to this comes primarily through aviation (FWIW) ... I hear “OH” primarily from older guys, and “ZERO” primarily from younger guys. I use “ZERO”, even though I’m not really a ‘younger guy’.
Well, I’m not the authority on this, like I said I was just going by memory, my first military service was more than 40 years ago, and my last was more than 25 years ago.
I would be surprised if officially the military uses oh for zero, anywhere, but unofficially it may become common usage in some areas that are more relaxed.
Remember that occasionally you could run into a guy that used “tin hut” for “Attention!”, although I recall the Drill Sergeants efforts to eliminate that phrase in basic training.