I realiesed that the "LivingHurtEvent" does not get triggered on a Multiplayer Server.
I tested this by using this Code.
@SubscribeEvent
public void OnKeyInput(LivingHurtEvent e) {
if(Minecraft.getMinecraft().thePlayer.worldObj.isRemote) {
Minecraft.getMinecraft().thePlayer.addChatMessage(new ChatComponentText("HurtEvent"));
}
}
On Singleplayer I got the message, on Multiplayer I didn´t.