I'm kind of baffled about what exactly docker brings to the table for OP. MC has a native Linux build that folks have running on most major linux distributions (Debian, Ubuntu, Mint, Fedora, CentOS, Suse, Arch, etc.), and a build that will run on ARM processors. So there's a strong chance you could just run MC on your slackware NAS no docker required if you worked on it.
If for some reason you can't get it running on slackware, you're already virtualizing windows, so virtualizing another linux distribution is trivial. Virtualize something minimal like a debian install with no tasks selected or Arch, and you can run the MC server there with very low overhead.
MC works great on linux, no docker required. Is the idea that docker would provide compatibility with proprietary NAS boxes? That would make sense, but OP is already administrating his own system and virtualizing windows, so that's clearly not his use case (or is it?).