I admit that it may be a black blade, but still I am inclined to believe that it is not.
Imo the black blade is not entirely dependent on your level of haki, and as noted in road to laugh tale, besides haki, something else is needed to create it.
Given which path Oda is taking with Zoro, this is the "relationship" of the swordsman and the sword, but since Aramaki is clearly not a swordsman, I don’t think that this is a Black Blade / Aramaki himself created it but then again, for the most part, my opinion is based on conjecture and I understand that, so I admit any of the options.