I have one scene where I have done all the gameplay related stuff. Now I am going to start work on the UI. Is there any way I can do the UI for my game using the interface builder in the XCode project which I get when I build from Unity? If yes, I will need to pass some info as to what parameters need to activated in the game scene. Can that also be done? Hope I am clear with my question. Thanks in advance.
You can do that, yes, but you'll have to set up your own custom messaging system for sending game data to the UI and back.
See this question for how to do that: http://answers.unity3d.com/questions/7298/cocoa-bridge-to-unity
didn't read it but i may help: http://technology.blurst.com/a-cocoa-based-frontend-for-unity-iphone-applications/
You may also want to look at this plugin: