Yes. Please note, however, that private wikis are not allowed. To be clear, "private wiki" refers to who is allowed to edit; not the nature of the wiki's topic. Therefore, you are free to create a wiki about your own personal fan series but you may not restrict the wiki so that only you (or you and a select group of users) can edit it.
Also, the term is "wiki"; not "Wikipedia". Wikipedia is the proper name of a specific wiki project. That particular wiki project is organizationally separate from FANDOM.