In the first scenario, I'd say the player whose ZoC is being moved into should be watching out for these things (as should you, obviously). But since such moves can't happen, the move never took place. Resolve it how you normally deal with mistakes (I'd recommend either doing the move again or moving the units to the nearest place they could have reached without entering the ZoC).
The scout trick you mention is one of the most useful features of scouts.

Though really any overwatch formation that you do that to is probably going to shoot you, if only out of spite.
