At present box config set server.defaults={trayEnable=false} will hide the server instance from the MacOS menu bar but has no effect on the dock. The icons that end up taking space on the dock also have no real use. If you have multiple instances running, there's no way to distinguish them on the dock and the context menu for them provides no controls for the instance like it does in the menu.
Not even sure there is any value to the icons in the Dock but would at least like a way to disable them if they are going to stick around for some reason.
FWIW there was discussion on cfml.slack.com about this code in runwar: