Is it okay to tile over rough wallpaper?

You will need to put up cement board before tiling. If it were me, I would remove the wallpaper and drywall. However, if that isn't possible for you then you should be okay. Make sure you screw the cement board tightly and even.

If the wallpaper isn't flat, as in it has raised designs, that might be difficult to do. If it's rough as in you've sanded it, that might help the tiles adhere to it.

I would try a small area first. How long do you want the tile to last? The shorter the time, the more it is worth the risk. For a permanent solution, use quality methods and materials.