It's the other way around. Normal mangakas are moonlighting as ero-manga artists (or someone else's drawing assistant), during their "free time". I mean, they gotta feed themselves while working on their own serializations. It's the same reason why some voice actresses goes by their pen names or choose to go uncredited, when they're voicing lines in an eroge to make ends meet. They're all getting paid a pittance afterall.

I've had my fair share of "hmm, I know that art style" moments, when I read normal mangas and recognized that some authors literally have the same art style with the ero-mangas I've read before. Knowing the kinks of a certain mangaka is definitely an awkward moment. It might be an open secret, but never mention it to their faces. That's in poor taste, even as a bad joke.

Needless to say, kinkshaming is also a major faux pas in our community. "Live and let live" is the golden rule.