To me, canon!Voldemort doesn't seem like much of a virtue ethicist even in the relevantly expanded sense. More of a consequentialist.

I had the same impression. I think it was Eliezer's-characaturization-of-canon!Voldemort that was the virtue ethicist. Voldemort harnessed, encouraged and exploited a form of virtue ethics in others to reinforce his own power. Tom Riddle was perhaps more of a virtue ethicist. As they say, power corrupts - it even corrupts away virtue systems that were fairly abominable to begin with.

I did upvote the grandparent despite this possible exception.