Yes interactive upgrade is always an option but its bit painful if you have 10+ hosts...
back to the and of vua.log there is a warning:
WARNING:root:Couldnt load esximage database: Cannot merge VIBs Dell_bootbank_OpenManage_7.4-0000, Dell_bootbank_OpenManage_7.4-0000 with unequal filelist attributes
So I would recommend try to locate and remove this VIB by:
esxcli software vib list
esxcli software vib remove -n <VIB name>
reboot and try to remediate host again...
If above steps doesn't help try to perform full VUM reinstallation see more in this thread:
https://communities.vmware.com/message/1880437
If you do not want perform full VUM reinstall another option is to reinitialize VUM database !(This will completely erase VUM database inculding existing baselines)
Besides above I have additional questions:
what ISO image have you uploaded to VUM custom or standard iso image...(post link)?
Are you using Dell Open Manage?