By RAW, it would not apply. Sneak Attack does clearly state that an attack roll of some sort is required. Even the secondary part that states, "You don't need advantage on the attack roll if another enemy of the target is within 5 feet of it, that enemy isn't incapacitated, and you don't have disadvantage on the attack roll." has it. Piercing Arrow is a Dex Save for damage ability and doesn't require an attack roll. So in the most literal text of the rules the answer is no.