But FOW doesnt hide sound or trees crushing etc, amount of times I have hit a repairing vehicle through FOW because I can hear it is uncountable. I know what you are refering to though, just making it clear so that people that don'nt know about this might see everyone as a cheater for FOW 'snooping'.
I agree once the vehicles hit the field, but when a game starts I personally don't look around in FoW like that. I wrote this from my own experience, as I don't use tact map and I found some of the replays very suspicious, like he was trying to just take a quick peek but not being too obvious.