It replaces the models of those green animated UI elements around a map with more natural models of people or hides them completely. Thus, it removes foreign elements from a map and makes the game look more realistic.

You can try to stop near them, sometimes this also works. But generally – yes!

I could shift them to the side, but:
1. these models are placed on a map in random orientation, so you'll never know to which side;
2. it could cause them to collide with other objects.

Yes! It works with everything! (except for similar mods, of course)

As far as I can tell from ATS demo, this mod is not fully compatible with ATS. It's not hard to make it compatible, but I don't plan to make any mods for ATS because I don't have it (and so can't test and upload to its Workshop).

If you want this mod for ATS, there is a similar one on the internet.
(or you can make your own )

This is an engine limitation. There should be no shadow from objects representing GUI and the engine simply ignores it, even though the models are configured to drop it.

No. I didn't place them on a map, I just changed the models, so they stayed where they were. There are map (or prefab) makers who placed them like that!