We actually built the app using Appcelerator Titanium. We modified Backbone to work with Titanium's API, and were able to reuse pretty much all the Models we wrote for our web app.
If anyone's interested, I'm thinking about writing a dev post about our experience. Definite Pros and Cons, but the TL;DR is:
There's pretty much no way we would have been able to do what we did in 2 months if we had started from scratch in Obj-C.
