Well, it's in beta right now anyway, and only then on Ghost(Pro) - https://ghost.org/help/social-web/ . Give it time.
EDIT: I kept reading and at the very end it says it's open to all customers... is that self-hosters too?
BUT, there is this line in the middle of the article "At the moment, short-form posts that you publish here don't show up on your website. They just go out to your followers on the social web." So, try following someone first, then post. Feel free to follow me @shane@social.futurnumerique.com. Let me know your handle, I will follow you, and when you post from your Ghost blog I'll try to see if I can see it.