We are using Socket.IO for websockets and (with multiple dynos) it seems to work fine when testing locally, even between different machines, just as long as they're on the same network. When we connect between 2 remotes the sockets don't signal.
Our implementation is fairly simple, with Node 0.10.26, Express 4 and Socket.IO 1.1.0 (tied to express).
The code itself is almost directly off the Socket.IO docs, the server is very simple with a handful of listeners and default config, the client auto-negotiates with and io.connect().
Modulus.io says it supports socket.io and like I said, it's working when I'm not jumping regions. Really wondering if there's some specific configuration that needs to be implemented to get this working across multiple dynos.