While it's understandable to want some kind of reference for canons you're unfamiliar with, fan wikis, especially for obscure series, can be incomplete or inaccurate, with fan theories getting presented as fact, and less popular characters having minimal or no information, even if they have enough canon to be considered appable.

I think that you could give applicants the option of indicating if they don't consider the wiki for a series reliable (possibly in the special notes section, if you don't want to add another section to the app), and then find another way to verify that the app isn't wildly off base. (Maybe find another player familiar with the canon and ask for their input? I'm not sure)

EDIT: Another possibility- if an app is for a relatively obscure canon and the applicant doesn't feel the wiki is reliable, maybe allow them to link their own write up in the Special Notes section? And make it clear on the app page that if mods aren't familiar with a canon, they'll consult its wiki, so players can have a heads up that they might want to indicate if they consider a wiki accurate or not.