There is no other way than reseting the root passowrd ..with the same method method followed for Linux passwd recovery.Since you are in the process of migrating its better you shut down the VM and move it to the other hosts and follow the steps for upgrading VM hardware,Vmware tools and then Power ON.
Once the VM is back in to action you can try out reseting the passwd for the ESX
Is there a file /etc/passwd-pr/etc/password.OLD on diskl. If so you maybe able to rename it back to /etc/passwd once you can login as root again.
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