Well, usually Yorkies that come from show dogs do well in shows themselves, but I'm not familiar with Fly Ball at all. (Just looked it up for anyone interested:
http://www.max200.com/flyball.htm) Looks like an obedience type course? Yorkies are prone to joint problems, but I would venture to guess that jumping on grass is better than jumping on hardwood floors. Sounds like fun though, Yoda jumps a whole lot around the house, up and down the sofas, and up onto the bed too..