Who is Onihime talking about in this scene? Is it a 4th wall joke?
The subtitles in the screenshot are not exactly accurate. Onihime warns that 「各方面」(kaku houmen = all sides, from every quarter) will get 「うるさい」 (urusai = noisy, loud, possibly cause a ruckus). It seems that Enki is threatening to rape Karin (from Enki's perspective, it would be heaven, but since Karin is protesting 「いやぁ！やめて！」[iyaa! yamete!], that would constitute as non-consensual). Therefore, Onihime warns that everyone would get noisy if Enki went through with it - meaning that either 1) Karin's 「仲間」(nakama = comrades, friends) will be indignant about it once they find out, 2) viewers will object with a loud complaint, or 3) the hentai viewers will make some other sort of noise... Her next line recommends for Karin to pray that her nakama will arrive soon, so it is very possible that kaku houmen refers to them.

It doesn't look like Enki's eyes are looking directly at the camera in the next shot, but rather at Onihime, so no, she does not break the fourth wall.
In summary, Onihime rather than Enki might break the fourth wall by alluding to viewers, but it is not clear enough that she is not referring to an objection by in-canon characters.