Just to be clear, 'Vietnamese nationals' (Vietnamese citizens) is not the same as Viet Cong. There were plenty of Vietnamese fighting against the Viet Cong, neutral, or switching sides.

As you say 'injured by their own booby traps', I'm guessing you mean Viet Cong, or people living in areas under their control. In that case, not often. These units were embedded in the area and therefore knew it well. The placements were strategic, either to target where they knew ARVN or their allies would travel, or to secure their compounds. In other words, they were not placing them about at random, hoping to get lucky.