I’ve been using Apple’s emoji in my apps for a few years now, not the smiley faces, but the system like icons as they’re easy to add into places where it gets more awkward to mix text and icons. Now that’s a rejection reason.
So if you use Apple’s emoji in your application and want to ship on the app store, you can only use it in a text field that the user can edit.
I was using some of the ‘object’ icons (and in our greetings card application, a whole lot more). But you cannot use the smileys, so you must use your own or a 3rd Party.
My understanding is that Apple is asserting their copyright over their emoji characters. This would include anything that Apple consider emoji (which IMHO is a gray area). I think that you’ll be okay with accented characters and I would image ‘arrows’ should be accepted, but I guess any of the emoji that looks like a graphic in Apple’s emoji style is what they’re going after.