Could the High Sierra root bug have been exploited over SSH? I'm sure we're all familiar with the recent security issue in High Sierra/OSX 10.13. It is well known that remote access can be gained using Screen Share, but I've not seen anything definite regarding the feasibility of a similar exploit over SSH, so:

Could this bug have been exploited over SSH, either with the default settings or after changing them?

(that is, attempt to log in over ssh as a nonexistent root user, thereby creating the root user in the same manner as when exploiting in person)

My thinking is that this shouldn't be possible by default, as the default sshd_config PermitRootLogin is probably set to no, but I've seen comments that suggest it is possible sometimes, which strikes me as being much more serious.

I don't own a mac, so I'm not able to verify for myself.
The login mechanism for SSH and for Aqua are two entirely different things.

sshd is the OpenSSH daemon (what allows you to log in via SSH) is sourced from BSD.  This vulnerability doesn't exist there.  

Additionally, the default configuration for OpenSSH is to disalow the root user to login whereas this bug/flaw allows you to log in as root with no password by simply pressing a button twice.