The reverse seems to be true! Dancing works well for people with parkinsonism because the music works like a cue (an external stimulus that makes moving easier). The positive emotions of the music probably help too. It's a good way to stay physically active. By practicing passes, for example during backward steps, the balance may also improve, but the latter has not yet been scientifically demonstrated. Dancing is probably a pretty safe activity because there is often a dance partner around that can help you if needed.