In theory, you can make any sound that you want. The results aren't very interesting. You can draw a sine wave and it sounds muffled. Add some jagged edges and the sound starts to sound more raw and high pitched. But it's okay to demonstrate what a sawtooth vs. sine vs. square wave sound like.
It would be a better to be able to draw in the time vs. frequency domain, using standard brush painting tools. Thay way you could come up with more interesting waveforms.