An admin can see hidden forums simply because he is the admin. You mean that you selected the hidden forum for "Display in forum"? If this is the case, the forum is not supposed to inherit anything from the hidden forum, just supposed to be shown there.
I don't know how it can appear in the moderators forum if it's not supposed to, because then you wouldn't be in the moderators' forum in the first place. If you mean that the forum is ALSO appearing in a forum list OUTSIDE the moderators' forum, you need to set the wiki forum's Display Order to 0.
If you are referring to "Last Post by" links, make sure that the wiki forum is hidden as well as the forum it appears in. If that doesn't work, there might be a bug somewhere. If you are referring to a wiki link (a link to an article) in an article contained outside the moderator forum, that links to a page inside the moderator forum, there is nothing that can be done to stop it from appearing. The user will receive a no permission error if they click and everything else is functioning as it should.