You are right, Dirt only backups the data, and if the TSP upgrade goes wrong, you just need to install another version, just make sure that the version that you are installing is compatible with your Unity and CCM versions:
My advised will be to have to different versions of TSP in case the anything goes wrong with the version that you have ;)
Or you can use any of the supported third party agents in order to backup the whole server (like disaster recovery with NetBackup), but check the capability towards Unity before installing non Cisco software.
Are you getting this error “Installer User Interface Mode Not Supported. The installer cannot run in this UI mode. To specify the interface mode, use the -i command-line option, followed by the UI mode identifier. The value UI mode identifiers...
The below trick might come handy when you have to add a new node to a cluster but you don't have or is unsure of the security password for the publisher. This procedure has been around for ages.
1) Login into the CLI of the Publisher.