It depends on task though. Selection is easy to do using eye-tracking as you just have to shift your attention onto the object long enough to click.

Drawing is a task that is more like aiming - attempting to hold your gaze at a precise location for a period of time. It is possible, but you are fighting against the natural saccade pattern of your eye and it becomes tiring very quickly. You can expect fatigue / eye-strain within a few minutes.