In the case of Mussolini, it turns out that the value system he adopted "valued" being imposed on others. But the quote you found suggests that he might have known this in advance - before he knew anything concrete about the value system he would adopt. That's not something that moral anti-realism says you can know in advance.
More realistically, it's likely that Mussolini choose his value system with knowledge of the contents, and specifically picked one that called for it to be imposed on others. But using this quality of the moral system as a litmus test for whether to pick it is not justified by moral anti-realism. Mussolini asserts the contrary, which is why I question whether he is using the label "moral relativist" appropriately.
I don't quite think he asserts that. He merely claims that fascism is at least equal to anything else in measure of consistency with relativism. But I'm not too interested in the finer points of Mussolini interpretation. I'm mainly putting him forth in answer to your interest in non-moral-realist tyrants.
From Being a Realist (even if you believe in God):
My mother, who doesn't call herself a theist (I think she's agnostic), doesn't even accept realism. She doesn't even agree with this:
That's little more than tautologies here. Yet it elicited an impression of being forced to believe. I know because she told me about the totalitarian dangers from such narrow thinking.
I'm happy to have finally found the root cause of our ongoing disagreement, but now, how can I deal with that? It looks pretty hopeless, but just in case, does someone have a suggestion, or should I just leave it at that? (My ego doesn't like it, but giving up is an option.)
Now I'm relieved to know that in near mode, she's a complete realist. This craziness only shows up in far mode.