I just tried it and it does seem to be working with push. Interesting...
Edit: I do notice that the options for Gmail is Fetch or Manual. And then the options for Fetch are Automatically, Manually, and a few time intervals. When Automatically is selected, the note at the bottom states "Your iPhone will fetch new data in the background only when on power and Wi-Fi".
I turned off wifi and it doesn't seem to be pushing, so I guess it's not what I was hoping for with real push for Gmail in native Mail.