Yes, it’s totally possible, as discourse is just an ember app on top of the rails api.
I think it’s a terrible idea, as you’ll just be duplicating thousands of hours of work. That said, I had a client who did just that and they seemed happy with it. I haven’t heard from them in a long while; I don’t know why.
The good thing about the approach is that at any point you could just decide to switch to the discourse front end. Edit: Or, perhaps, use discourse after the migration and then never get your app good enough to warrant moving to it, or allow users to choose which front end they prefer.