How can I insert Emoji into my Keynote presentation?
From Keynote's menu under Edit » Special Characters, I can see the Emoji characters and drag and drop them to Keynote. But in Keynote (5.3) they become invisible!
At the moment, this is not possible.
Apple's Color Emojis are quite new in the way they are rendered, and applications may have to add specific support for them. Chances are you'll have to wait for a Keynote / iWork update in order to be able to use them.
See this blog entry for a few examples of what is already possible with Emoji: Abusing Emoji in iOS and Your Mac