Well, I've fired thousands of 7.62 tracers from M-240:s and HK G3:s and when you fire them they go straight as on curved rail (as you very clearly see them drop when firing at long distance... There is however NO "wobbly" tendency at all that is caused but the camera vibrating from the recoil and the shutter speed causing them to zig zag as mentioned earlier here (and that is also what causes them to look like lasers as the bullets travel a few meters in the time that the shutter is open (and shaking)).
When in a vehicle your head has very good dampening by flesh, fat and other organic materials from the vibrations as opposed to a camera that is rigidly screwed to the wing that is vibrating - and no - you don't see them zig zag:ing like a camera does. Have not fired tracers from a plane but I guess it's the same as from the turret of an APC

Edit - or for that matter when you have you chin pressed hard against the stock of a wildly vibrating G3 that you have to hold very firm to not rise it while firing full auto...
Come to think of it I have fired from the air in the form of the door of a Huey Helicopter on an assault practice but that was only blanks unfortunately

The chopper was there to lift "wounded" and we persuaded the crew to lift some of us over the field in front of us where the b-force in the practice was. We skimmed the field that divided us and the enemy and landed in a clearing behind them with our G3:s at full auto. Mmm...