Absolutely sure. Apple is totally transparent about this being a requirement for them:

https://developer.apple.com/app-store/review/guidelines/

"2.17 Apps that browse the web must use the iOS WebKit framework and WebKit Javascript"

Gruber claims it is: http://daringfireball.net/linked/2012/06/28/chrome-ios

I'm also sure. At least for mobile devices. I can't speak to desktop Chrome. That's why it does the same weird rendering Safari does which has become more noticeable since the split from webkit.

There's one discernible difference between Chrome and Safari on iOS 8- try scrolling on both and you'll see that both render them differently. Much faster on Chrome and less so on Safari. Prior to iOS 8, scrolling on both browsers were very much the same.