Sure, the perfect mobile person is someone who has a deep understanding of the code and incredible design skills and taste - but what you're talking about is a unicorn. I'd be surprised if there were more than a few dozen of these people in existence.
Here in the real world your choices are:
- Mediocre-to-shitty engineer with solid design skills. He/she will shit all over your codebase and mask a boatload of technical debt by how beautiful the app is (until your crash reports roll in, or it's time to add features).
- Good-to-great engineer with mediocre-to-shitty design skills. He/she will create a solid, stable, extensible codebase but the app will range somewhere between "buttons goes in right places" and "buttons WTF".
On the other hand, there is an increasing demographic of designers who do understand the ecosystem. I'm lucky enough to work with some of them, who understand the nuances of touch target sizes, gesture-based control, etc. They're a little harder to find than your typical web designer, but they're a hell of a lot more common than your unicorn engineer-designer-fused-archon-deity.
A good engineer pairing with a good mobile designer is a combination far easier to achieve than hunting a near-mythical figure.
"near-mythical" huh? Good to know.