As of today, there is official mod clearance for The Wizard of Oz and all related materials to be freely unmetaed. Considering the
ridiculously pervasive nature of the canon as well as certain arguments for
Oz as America's secular mythology, Ozian canon in all shapes and sizes is going to be treated like mythology and legend with the similar understanding that
what they know could be off from reality. So the flying monkeys and the Yellow Brick Road and 'I'll get you my pretty', the 'munchkin's and 'no place like home's, the witches with big conical hats, the 'Boy from Oz', the 'man behind the curtain', and the million other little references,
etc?
Go for it.