You know how you can't pre-place units on the edges of the map? Can you create units or move units into that area in-game?

Uh... The reason why you cannot put units on the edges is because you are actually placing them OFF the edges, you can get units just as close to the edge using triggers as you can with preplacement(without crashing) or walking there.

You move units outside of the map when you want them to stop moving. They don't actually move there.