An add-on that customizes your user interface or provides you with helpful information is almost always permissable. Add-ons that play the game for you in some way are not allowed and can result in banning (for instance there used to be an add-on that would automate fishing for you so you could fish without having to actually do anything yourself, Blizz frowns on anything that takes away the key-pressing experience of actively participating). A lot of the more successful and popular add-ons actually had their elements and features incorporated into the game over the years.

I'm unfamiliar with any type of "maphacks" or whatever that means. So I can't tell you what category it falls in. You can probably figure it out for yourself.