You're vastly underestimating the scope of Germany's laws regarding the Nazis... you could literally write a book on the subject. Suffice to say: they've got rules for every depiction, even historical ones.
Media for example can't include nazi iconography without very explicite guidelines, for example: video games essentially omit the swatstica et al
In any case, our video made in the US criticizing a Holocaust denier would not be impacted by those laws
I wouldn't be so sure... I forgot to mention that holocaust denial is illegal, holocaust denial INCLUDES arguing that it was on a lesser scale. I know you're not the one making the argument, but even depicting a person doing such a thing will offer you little protection.
Germany's very over the top on this subject. To the point that I think it's significantly detrimental.
Suffice to say: expect this to happen every time you cover such a topic like this. Either plan for it by removing all offensive materiel, or go into this understanding that you're probably going to get (unjustly) blocked in Germany.