Not easily. See Can Discourse ship frequent Docker images that do not need to be bootstrapped?
One explanation is that when the project started docker-compose wasn’t really viable, so they developed their own launcher. It’s what they use for their hosting and there’s no reason to change it. The install docs work amazingly well for people who know absolutely nothing about system administration.
I suspect so. And they seem to work for a bunch of people, but if you’re one of those people and something goes wrong, you can’t get (much) help here because it’s not what folks here know about. It’s unclear (to me anyway) what kind of support they can get elsewhere, but often there are exchanges like “To solve that problem, just do X” followed by “I can’t do X because I use bitnami and don’t know how to do that.”
That said, I’ve started working on creating images that are very similar to the supported images but can be deployed with docker compose and similar tools. I’ve recently considered making them as compatible as possible with the bitnami image so it’d be easy to move between them. What I have available isn’t quite ready for anyone to use, as I’m still changing things around; I’m not sure if it’ll be a couple of months or a couple of years.