It's really quite simple.  What did the Scarecrow from Oz want?  A brain.  He only wanted a brain.  And what do zombies want?  Brains.  It is my belief that Scarecrow was actually the first zombie.  And imagine what would have happened to Oz if, once the zombie virus really got hold, he had bitten his companions.  Would the Tin Man been quick with his axe and taken the head of Scarecrow before he could sink his hay teeth into Dorothy?  Would the Lion have swiped out Scarecrow's hay brains?  I tend to think not.  No I believe the real land of Oz is populated with zombie Munchkins, zombie flying monkeys, zombie witches and of course with plenty of zombie lions, zombie tigers, and zombie bears.... oh my.