You can use Ecamm Live to stream to a 3rd party services by pasting in a RTMP URL and stream key into the Custom Stream Key destination.

If you're trying this, and getting "Unable To Start Streaming An unknown error occurred", then it's possible your network is blocking the RTMP port (port 1935).

You might need to open this in a firewall on your computer's security software, or have an IT person open it on your network. 

This port is often blocked on public Wifi networks too.