Socket IO Server to Server

Yes, absolutely. Just use the Socket.IO client in your server application directly.

https://github.com/LearnBoost/socket.io-client

You can install it with npm install socket.io-client. Then to use:

var socket = io.connect('http://example.com');
socket.on('connect', function () {
  // socket connected
  socket.emit('server custom event', { my: 'data' });
});