Not only can they attack other members, but they can also fight NPCs. However they dont gain the bonus damage against other members that Soldiers get.

NPC Hunters are able to fight NPCs for extra Money and Resources, you can also loot "Presents" from the NPCs you kill such as extra money, weapons, and other goodies.

Note: NPC Hunters are the only profession that can find extra items, like Presents, and other good items that are unavailable in the Shops.

Tip: It is best to have armor before trying to hunt NPCs.