For web applications you can have one designer create a mockup, and then another one (Perhaps Off Shore) generate CSS, templates, themes, skins...whatever.
How can you do something similar with Monotouch? How would it differ from what can be done in SDK workflow?
Can you use some of the same tools as for WPF/Silverlight? (And still be like a native iPhone app).
MonoTouch doesn't use WPF or Silverlight at all. The virtual machine is similar to the Silverlight one, but that's where the similarities stop. MonoTouch uses Apple's tools for development, including Interface Builder, which is a kind of UI designer, and in theory would replace the WPF editor in Visual Studio or Blend.
In reality though, most developers prefer to simply write most or all the UI in code, because of the simplicity of the API. Designers need to work directly with the developers, not the tools, to make sure their design works and can be implemented.