The fix for this seems to be to enable automount in diskpart. I recall explicitly disabling automount so that my connected iSCSI VMFS volumes would not be brought online within Windows (which as I understand it, ruins the volumes).
Sadly, I do not have a Veeam server with connected iSCSI volumes that I can test on, so I'm hoping someone out there either:
1. Has a test system ad can test it
2. Didn't know about this and installed it without incident on their Veeam server
3. Could persuade Veeam to test it and get back to us in the weekly Veeam Community digest
