360 degrees scrolling isn't exactly true, what the mighty mouse actually does is vertical scroll in conjunction with side scrolling (I saw the insides of a mighty mouse). So, the question is really if you can have side scrolling on a guest OS using the Mighty Mouse, no, you can't (neither in PDM 3 or 4), side scrolling of the Mighty Mouse is only possible in OSX even if you use it in Windows natively you'll not have side scrolling cause Apple hasn't made any Mighty Mouse drivers for Windows so it uses generic mouse ones. Even the mouse I use, which is a Logitech V550 Nano that has side scrolling supported both in OSX and Windows (thru Logitech drivers) can't do side scrolling when working thru Parallels. Parallels team, please add side scrolling support to the Parallels Mouse Driver.
@Specimen, Thank you for an excellent response. I do hope Parallels adds side-scrolling support in the future.