But the issue is the deep integration. If I choose to send an email in iOS, will it send me to this gmail app or will it to send me to Mail?
It's the same issue with Google Voice.
It's the same issue with Google Voice.
I agree with this thread that this is one of the best things about Android.
There will probably be nothing special about the native app's compose interface, though, so I don't see that it will be a problem to keep the account registered in both clients, but only to sync regularly with the native Gmail app, and to use whatever app iOS picks (undoubtedly MobileMail.app) when composing.