I've seen a pressurised tank fail (not oxygen, but the pressure level and construction were similar). It had gotten a little ding on the side during transit and while we were filling it the entire side let go, the tank was propelled about 20ft and made a hell of a mess of it's surroundings.
I don't have any experience with aircraft pressure vessels, so I'll limit my comment on that to saying that if one of these oxygen tanks did rupture then it could easily cause all manner of problems, the energy in those things is amazing.