The idea that you have to be a "native person" or a "web person" is ridiculous. Let's just use the tools that make the most sense for the project at hand.
I agree if you're a company, you can't afford to turn your nose at one or the other. But there's few unicorns who can build excellent apps in all of web, Android, and iOS. And despite a lot of software mythology, I don't believe most programmers can just learn a platform in a few days, not to be seriously capable at it.
While you need your designers to understand both well enough to create a common design, you are going to find very few coders who are true experts at both Web and native architecture and implementation. While you can cross train people, you need experts in both.
Another way to look at this question is to ask under what circumstances would you expect a developer on X platform to shift to Y platform.
IMO it takes 2-3 months at least for a good developer to become professional-level in another language. And in an app context, it's not just a language, but a large set of libraries and frameworks.
So you can assume a 4-6-month ramp-up in skills, with relatively low productivity, and then work backwards to decide if the investment is worthwhile. If the developer has sufficient domain and institutional knowledge, and is likely to stick around, it might be.