As an administrator managing a vSphere environment, the last thing that you would want to do is share the root password. Remember, a forgotten root password cannot be recovered/reset and will require a reinstallation of ESXi.
Joining an ESXi host to an Active Directory domain will allows users from a particular domain user group to log in to the ESXi host without needing to know the root password. This not only eliminates the need to periodically change the root password, but also enables better auditing.