Welcome, Don.
Short answer is no.
You don't indicate what you have for a joist structure.
If the joist structure is adequate (see Deflecto in dark blue bar near top of page), and
if your joist spacing is 16 inches on center or less, and
if your boards are in good condition and well fastened, the absolute minimum you must do is add a layer of nominal 1/2-inch exterior glue (there is no exterior grade) plywood with no face of grade lower than C.
On top of that you can add the tiling substrate of your choice, such as your proposed CBU, properly installed per manufacturer's instructions. Then your ceramic tile.
My opinion; worth price charged.
PC
