Drew, You can, I mean, no one will come to your house in the middle of the night and arrest you. But putting ceramic tile on any kind of wooden substrate is a poor way to do it. Use a tile backer board such as cement bd., Hardibacker, or Denshield. You also need and appropriate sub-floor, i.e. minimum 5/8" plywood over joists no more than 16" oc. (designed for L/360 or better deflection limit).