Well I tried and failed then I found this here : https://helpcenter.veeam.com/docs/backu ... tml?ver=95
Veeam Backup & Replication does not support product upgrade in the unattended mode. However, you can:
Uninstall the previous version of the product.
Install a newer version of the product in the unattended mode. You must connect to the configuration database that was used by the previous product version.
Makes mass upgrading a little more complicated. I did try upgrading via the msi's but got hung up on upgrading the console, so probably best to do a full uninstall then install in unattended mode but the challenge would be making sure the configuration database's are all named the same, I'm pretty sure our's are but would need to do some testing.