When you look closely, it seems like the wound starts on his hand, unless it's supposed to be a cut that runs the entire length of his arm. As far as I know, Steam doesn't have any specific rules against including suicide attempts in games. I personally believe that Nika lost control and got himself injured, maybe he got into a fight with a group of guys or was hurt during an attack (possibly stabbed in the chest, which could cause a lung to collapse). It's all speculation, but I don't necessarily think it's a suicide attempt.