Presumably yes if it uses native APIs. On iOS, although .nib files are supported, people tend to prefer Ruby DSLs to define interfaces though. I imagine that something similar will happen on Android.

Expect that it won't be long before somebody comes out with a cross-platform wrapper for native UI elements similar to Xamarin 3.0.

Yes, XML based layouts work just like they do in traditional Android development.

And to chrisdevereux's point, we've already got some Android support in MotionKit.