1. Do ATGM and tanks need LOS to the target they are shooting? Or, can they shoot at something if a friendly unit has LOS to the target?
Of course SJ is right.
It's easy to get LOS and spotting confused, at least it was for me. Then I figured out a HEX (and any units in the hex)is NOT spotted unless it meets certain criteria (has a Move Marker, or an Assault Move Marker, or a Fired Marker, or is adjacent to an enemy, or is Clear terrain, or an enemy has made a successful Spotting Attempt, etc.) In simple terms, a hex (and the units in it) are NOT spotted, unless they are Spotted. It really does not matter if an enemy unit has LOS to the hex or not.
Now, a Spotting Attempt does require the friendly unit making the attempt be able to see the hex it is attempting to spot. And a Spotting Attempt is only made for a hex (and the units in it) that is not otherwise spotted. With the exception of Indirect Fire, to fire on units in a hex, the firing unit must have LOS to the hex, and the hex must be spotted (does not have to be marked Spotted if it meets the other criteria).