Is there a difference between hydrated oxides and hydroxides? My guess is that they are different. 

I think hydrated oxides would have a lattice with the cation and oxide anions as lattice points and molecules of water trapped in interstitial spaces, while hydroxides would have the cation and hydroxide anions as lattice points with no water molecules in interstitial spaces.
Hydrated oxide is a compound of an oxide with water. And Hydroxide is a diatomic anion with chemical formula OH− ( a hydroxyl functional group). you can refer to this link for better understanding : http://www.memidex.com/hydrated-oxides. Also looking at the definition of hydration might be helpful.