.dt, .sf, .salvo, .delay, .speed, all used regularly while actually in flight.
And SC2 players are widely recognized as freaks of nature in the gaming world.
And if you don't want the metagame to be available to all, it would be better if it were disabled entirely. But then you would still get guys like vDALLAS, or Ghi, or other old paranoid farts who will whip out a kitchen timer for that stuff.
IIRC, I've seen Challenge shelling a field from over a hill begin. I can only assume he is calculating the ballistics trajectory. That in itself is metagaming, yet it would be ridiculous to try and impede that through rules or game mechanics, since he's simply making use of a calculator, CD of the shell, initial muzzle velocity, and a protractor or software overlays.
I am curious as to how he measures height of launch, given that tanks don't have altimeters.