Are mortars and arty impacted by the reduced visibility rules? Do they only hit on grenades?
Unless the unit is an artillery firing on a TANK DESTROYER. In that case a STAR will also cause a hit.
WINTER WARS RULES p.8
When a Tank Destroyer targets an enemy Armor or Vehicle unit, all stars rolled score a hit. Unfortunately, they are also more vulnerable to enemy fire, due to their lighter armor: Any non-Infantry unit targeting a Tank Destroyer unit will score a hit on any star rolled.