well, hashing is a perfectly good way to build tonality, but scribbling is not. it's really incredibly difficult to hash with a wacom.
in general i'd say it's more difficult to draw something from scratch using a wacom, to the point that it's usually really obvious. if you want to build drawing skills i'd stick with paper and pencil, and save the wacom for what it's better suited for---shading and retouching.