Update: after about three hours the setup.exe and related msiexec did end without me having to taskkill them.
Explorer never did restart.
I then forced a reboot remotely and it appears everything is installed correctly as I surmised.
I am now running RemoteUpdateManager on the same lab machine and it too has gone into some sort of suspended state after finding no updates were needed.
I also have another thread open concerning issues I've encountered setting up the UpdateManagerServer.
Really I am starting to think that none of these deployment tools is ready for prime-time.