We are imaging using dockutil to setup our User Templates with new Dock icons. We are installing an empty Dock.plist gathered with Composer as the results were extremely unreliable without an existing .plist in the User Template folder.
We have our dockutil scripts completed and the icons are in postion with 2 oddities.
We are experiencing a 'Macintosh HD' icon being added to the right side of the dock despite there being no reference to Macintosh HD in the dock.plist or in the dockutil setup scripts.
We are also seeing a Downloads folder, belonging to our image development account. We include the command below, with no changes.
"$dockutil" --remove 'Downloads' --no-restart "/System/Library/User Template/English.lproj/Library/Preferences/com.apple.dock.plist"
You may have better luck just copying the com.apple.dock.plist file from dock.app to the User Temolate rather than packaging and deploying an existing dock.
Then when the default dock gets created for a user just remove all with dockutil then populate the rest.
I'll share my script tomorrow.