The latest Gentoo *minimal* installation iso images are shipped with the following message in /etc/motd: To start an ssh server on this system, type "/etc/init.d/sshd start". If you need to log in remotely as root, type "passwd root" to reset root's password to a known value. However, current sshd daemons do NOT allow root logins unless PermitRootLogin is set in /etc/ssh/sshd_config. So the motd in the Gentoo iso confuses the user. A quick fix would be to add 'PermitRootLogin yes' in the image.
I confirm this bug in install-amd64-minimal-20160218 .
*** This bug has been marked as a duplicate of bug 573808 ***