no, you can do easy lvl and you unlock the same song but you can unlock bonus songs when you complete like the lvls and get certain stars. If you complete easy with all 5 stars you get some bonus songs. hehe, i just used the cheat to get all songs and items lols.
I havent played it for a while, taking a break. Hehe, but i cant seem to get the transition from medium to hard. I still have to practice. Hard is freaking hard!