If you’re looking for the official word on using Docker, you can see here:
For self-hosters, the Ghost team recommends using Ghost-CLI on ubuntu. This is the only setup where we provide support & fix bugs.
The Docker repository is a community lead project. We aren’t in control of updates nor do we provide bug fixes or support, but we do list it as an option because it’s a popular, active project.
The choice of how to run Ghost is really down to what you’re comfortable with and what level of support you’re looking for.