How to curve type around a circle using keynote?
No, there's no text tricks like that built into Keynote. 

In order to achieve effects like this, you'd have to use ArtText or TypeStyler.

If you only do it once and for short text you can use the CRUDE way:

In a crude way and for short words could you make a number of single letter text boxes? Place them where you want them, go to metrics (the little rule) in the inspector and rotate each one to suit.

Or use WordArt