Esther, If they are procedurals, they would have to be converted to another format anyway, unless they are for carrara which might not make sense anyway. People could texture their own. You would probably alter them anyway. It would be safe to ask, but procedurals are really kinds presets, so it is tricky, unless you just flat out try to pass off a preset as your own.This would be wrong, but honestly you have a hard time showing that you didn't create it unless it had some pretty unique options. They are a sticky wicket to distribute in many cases.

No need to think outside the box....
    Just make it invisible.