When installing a three node cluster you would still need to be root in order to configure passwordless-ssh (publickey) between the nodes, or to itself in a single node setup. For a data repository cluster, passwordless ssh is a requirement when installing the vertica database. After the installation of the vertica database, you can remove the root passwordless ssh config, but you would need to re-enable it when doing a subsequent vertica upgrade. To remove passwordless ssh for root, you need to remove the ~root/.ssh/authorized_keys* files (if it only has entries for the 3 nodes), or remove the entries in the ~root/.ssh/authorized_keys* files for the nodes in the cluster
Note that the passwordless ssh for root must be set up as the root user.