Darkin aren't Void. The Darkin we know look like they do because they are twisting the forms of their hosts to resemble what they once were. Which based on stories was even a twisted form of their glorious self because of magic.
Not the Void.
The answer is no.
As Jaspers says, Darkin arent Void... and they were not corrupted by the Void, they were corrupted by the death of Azir, literal corruption after the empire was left without head.
Aside from that, A Void Renekton skin would look like a "purple monster with many eyes" or something like that, in other hand, a Darkin Renekton would look like some kind of "full armored demon crocodile"... the point is that the visuals of both things are different.
Personal take on it: Darkin were morphing their own form and flesh to become more weaponized with or without the void influence. Aatrox has a bunch of lines where he contemplates if he has been effected by the void. If his physical form clearly showed signs of Void corruption, it wouldn’t be a question.