Interestingly, most of my experience is in c#, but I've now got a side project that requires apps. I wrote them in Android and iOS. I looked at Xamarin as well, but I couldn't see the point of learning essentially a new framework. I figure whatever pattern you use (probably MVC) it will be the same on both. And the layout paradigms are different between them, so how is Xamarin going to fix that? My solution was just to use webviews instead of the native layouts (decided after bashing my head against both layout engines).

Anyway, my point is once you understand how things are organised, the language shouldn't make much of a difference. Especially not between popular, run-of-the-mill languages like c#, java and ObjC. Your devs could probably learn iOS pretty easily.