Keynote Build loop

I don't believe so - I did some lengthy searching a few months ago and found nothing. The best suggestion that I read was to make all of your looping stuff and then make the entire slide a link to a separate keynote file that contains the rest of your presentation. You can add a box and send it to the back of the slide (as the background), then you can link that to the new presentation, and link all of the other objects as well. Then when you want to move on in the presentation, you just need to click anywhere on the looping slide. It's not the most elegant solution, but it's worked pretty seamlessly for me.

Good luck!