Fan art is not limited in the same way, as the famous 4kona demonstrates (unfortunately, I do not have the untranslated original). I saw way more of the same, and the remarkable part how imbalanced this is. Neither is prominent at all (either because of the official position, or because all such stuff is carried by lunatic fringe), but nazis outstrip commies 10 to 1.
I mention this because, in the U.S., the same ratio is 1 to 100 -- in the opposite direction. Nazis are officially designated as "not OK" by the establishment (a position I support wholeheartedly), when commies are admired by large number of people. And some of these people have influence, so Lenin is studied in most colleges. For the benefit of those who escaped the contact with the liberal education, Lenin is the author of, among other things, the hilariously confusing telegram which ordered to "round up and execute prostitutes inebriating soldiers and former officers" (he obviously meant to execute both prostitutes and former officers, and not just prostitutes who inebriate former officers).
The popular love of communism in this country -- and most of all, in local universities -- was the most unpleasant surprise which I received as an immigrant. After all, commies wasted far more people than nazis (and continue doing it in NK today). Perhaps lower casualities in the Cold War and Vietnam made Americans think that commies were not as bad as nazis, who had to be fought in the old bloody way.
I do not suggest that Japanese on the whole are any saner, but it's something hard to miss if you see any anime.