Question about dev Unity ios with an existing xcode project

The question I have is how to take whatever unity iOS output (lets say, done by graphics designer artists/animators), and "incorporate" into an pre-existing xcode project. Or vice versa, take whatever coded in the xcode project (ie. objective c), and bring in the output from Unity (i assume it will output a gigantic xcode project with generated code in c/c++/objective c) since thats what has to be compiled to generate the .app bundle for appstore?

I am new to Unity3D and I am doing some high level tech investigation to decide between using cocos2d/3d or Unity. The answer will definitely impact what we think the workflow should be like. If someone can provide documentation bit or short tutorial to highlight this, that will be great. It is also possible I am misunderstanding the whole thing...