Chrome IOS - Is it just a UIWebView?

No, it is not just a UiWebView. Mike Pinkerton's post on chrome-team googlegroup:

Chrome for iOS has some pretty major technical restrictions imposed by the App Store, such as the requirement to use the built-in UIWebView for rendering, no V8, and a single-process model. As a result it’s been challenging to re-use critical Chromium infrastructure components. That said, there is a lot of code we do leverage, such as the network layer, the sync and bookmarks infrastructure, omnibox, metrics and crash reporting, and a growing portion of content.

The networking layer alone contains a lot of optimizations to enhance your browsing. Here's a quick overview: http://www.igvita.com/2012/06/04/chrome-networking-dns-prefetch-and-tcp-preconnect/

As of version 48, Chrome for iOS uses WKWebView, which is the same view used in Safari.

Sources:

• Chromium Blog
• Ars Technica
• VentureBeat

Yes, you're right... it uses the webkit rendering engine, with Chrome UI.

Ref. DaringFireball...

It’s not the Chrome rendering or JavaScript engines — the App Store rules forbid that. It’s the iOS system version of WebKit wrapped in Google’s own browser UI