Well some people have written their fan stuff here ¯\_(ツ)_/¯

Well, in my opinion, they shouldn't

Wait Nvm. Their fan chars shouldn't be on fandom at all.

If its on fandom they don't own it because it's a wiki.

Well in my opinion fandom = fan dom. The word fan is also in fan character.

Also this wiki is basically based on fan ideas

Ummm no

This wiki is mostly cannon stuff

I will make an example:

A person make a book, and to have more fans he say that fans can make their own characters in the story, so the book become famous, and a big fan start a wiki (a place where put all information contained in the book). People to make know their characters start writing them in the wiki, so the owner of it create a page just for that.

For me it seems legit.

Maybe is not an example but more a summary, but I hope you got it