Absolutely. My primary concern is with the controls feeling native. Reimplementing controls with UIViews doesn't seem much better than reimplementing them with HTML/CSS (save for performance). There's still surface area to break the illusion.

Some food for thought: what if you kept HTML and CSS but instead of using a WebView to render it, you rendered the DOM manually using UIViews? You could even make overflow: scroll; turn into UIScrollViews automatically.