I never heard about that aspect of the battle of Monte Casino.
The Goumiers did superbly in breaking the right flank of the German line, across the Liri valley from Cassino, flanking the whole German position. The Moroccans were excellent mountain infantry and experts at infiltration.
The problem of course was exactly as said, they were barbaric and could not behave themselves among civilians. The French used them again in the invasion of Southern France, Operation Anvil, and then they started to replace most of these Colonial troops as fast as they could, sending them home before the winter of 1944-45. New French recruits from liberated France took their place.