Board Thread:General Discussion/@comment-27954638-20160311070306/@comment-1757994-20160311212734

Wikia IDs are Wikia-wide (capital W). The specific Wikia site (wiki, lower w) where people create their IDs is irrelevant.

So someone can create an ID on any Wikia wiki and contribute to your site or be an admin there (or not, depending on what the admins on your wiki choose).