I’m pretty sure if you search this forum there is a topic about installing Discourse using this method. Just googling Docker Hub and searching Discourse results in this repository (which I’ve not used and am not suggesting for use)
I believe the requirement of using the ‘official installation method’ is with the expectation of support. Civilized Discourse Construction Kit, Inc. provides support via this forum for the ‘standard install’ which I feel is very generous for software which is basically free. But this forum is also frequented by many knowledgeable individual who will help folks with ‘non-standard installations’ I believe there is even a ‘un-official install’ tag to filter for such topics.
You just have to keep in mind, you are treading into the undocumented realm. Here be dragons