To my knowledge radar cheaters are now dealt with by not sending information about enemy positions if they are behind walls. It's not a perfect solution ofc but it seems like it works reasonably well.
Depends, there are many methods of doing it. Many games let you hear gunshots/grenades/etc.. that are far away. You can use those sounds to show a radar spot.
https://www.youtube.com/watch?v=ATkpqYmWt8k&feature=youtu.be