To reproduce:

Install RHEL 7 public beta. While package install is proceeding, create a user account and check the 'make this user an administrator' box. Do *not* set a root password.

anaconda will let you escape the install like this. Now, boot the installed system. If you do a minimal install, you go straight to a login prompt; if you do a larger install, initial-setup may run, but I think it does not require you to set a root password.

log in as the user you created. Now, try and do an 'administrative' task, since you are an 'administrator': 'sudo su'.

"(username) is not in the sudoers file. This incident will be reported."

At least in a non-graphical install you have now shot yourself in the foot, you have no access to admin privileges.

In Fedora, 'administrator' users are put in sudoers, so just having an admin user is sufficient to ensure you will be able to access administrative functions. But I guess this is not the case in RHEL. If that's not changed, anaconda should always require you to set a root password on RHEL, or else you can lock yourself out.