Most of the big problems I have with CSS (as a daily user) come from supporting multiple browsers, and dealing with their variable output from the same CSS files.
If the CSS syntax is used as a way of declaratively describing styles in a single controlled environment (iOS) then that's not the same thing, and I would think that it should address a lot of the headaches that browser-based CSS currently has?
Plus it would (hopefully) allow the use of existing tools like LESS or SASS to provide even more control and re-use in creating the resources that go into building your iOS app.
I don't see any reason why LESS/SASS wouldn't work, provided they've ported the majority of the actual spec (comparable at least to any browser out there). Since they simply compile your code into longform CSS it doesn't actually leave any footprints.