OpenVPN is a network-based topology. If you would introduce raw-datatraffic in the same tunnel, you loose all of the addressing-capabilities here as the unix-sockets and pipes don't know how to "address" the other endpoint.
If you would transfer raw-data over a normal network, you should learn your tools some ip-knowledge or wrap them into something like
netcat:
Server:
cat /dev/source | nc remote-ip port
Client:
nc -l port > /some/where/dest.file
