I weary of purchasing a ps2 to ps3 controller adapter because I wanna play GH: World Tour on my ps3 but I am trying to avoid purchasing the entire set , since I already have a GH:3 controller for ps2. So would it work?

If the PlayStation 3 controller doesn't have any additional features, you can use any PS2 controller adapter. In fact, the GH Guitar Controller is just a plain old controller slightly altered - the game knows it's a guitar because it keeps the left button 'pressed' (in fact, 'shorted') all time.