As Dag Nabbit stated, a Minecraft server does not talk http. You would typically do this via NAT. A proxy server needs to know the protocol, because as the name suggests, it acts on behalf of the the client. Nginx knows various protocols, not just http, but Minecraft is not one of them. You can however write a proxy module for this protocol and use the existing nginx infrastructure. Since I'm not familiar with the protocol, I can't comment on the fact that this would have any advantages over NAT.