At my school, there is no specific rule about having so many credits in order to participate at graduation. A senior files for his/her degree with their own respective colleges, and signing up for the graduation ceremony is something done separately with the Bookstore. The bookstore gives you graduation instructions when you purchase your cap and gown.

And then there are students who chose to not walk at all.

My campus has a winter, spring, and summer ceremony. The spring one tends to be the largest--mine had 1316...and each student was called by name. That's how I got to sleep for 20 minutes.

So basically...anyone can participate in graduation. I don't know why anyone would want to if they're not really graduating, but oh well.