Well, there's been arguments put forward that this sort of thing is a "fork" that does indeed harm Wikipedia (and perhaps the forked wiki too) by subjecting both to contributor drain - if the two wikis were merged they'd each have more people working on their contents. I'm not so sure about this, but I nevertheless think it's probably a net loss to be deleting content from Wikipedia that's perfectly acceptable for other encyclopedias to cover.
The problem with this is, that Comixpedia is a collection of all webcomics they can think of there's no editorial control and literally anything can get in. Merging that with Wikipedia would introduce scores of what are basically vanity articles for the creators. Just try arguing for undeletion with a solid claim backed up by references.
--Mgm