I'd be curious to know how the trackball games (Centipede, Millipede) work on the iPad. Spinner games like Tempest and Major Havok could be a problem as well! Still, very impressive collection and the packaging is fantastic.
I think a virtual trackball/spinner controls will be very easy to create. Just have a circle in which you can move your finger for precise work, or swipe/spin like a demon for more widespread attacks. It should be easy to program momentum into the controller.
FWIW, scrolling a web page has worked like this (i.e. with precise location or rapid swipe-scrolling) from day 1.