Hey, sorry for the late reply.
This is how I have it set up: I have a flask RESTful API server with an endpoint which takes a POST request thst includes an identifier for the bot, an identifier for the client, and the message. When a request is received, the flask app will look at the identifier and query the Rasa bot using the Rasa python API. The response is then sent back to the client. For specifics on the Rasa API: Agent
So to answer your question of whether I have flask and Rasa running on the same server, the answer is yes since Im running Rasa from within the Flask app. The above link has more info on which methods to use.
Let me know if you want anything clarified further.