After clarifying the eromanga and doujin wiki pages a bit, I realized that the doujin tag is used for non-pornographic fan-comics as well.
I see no reason why it should be reserved for adult works, either; simply rating the "offending" material as Explicit should suffice for differentiation.
This leads me to question whether the eromanga tag is needed at all, since a simple comic rating:e string works just as well.
Updated by jxh2154