I believe not, XAML and HTML / CSS are separate paths when it comes to presentation level, and you cannot mix them (except for the “dirty tricks” like the WebView control in XAML, but it is not used for reuse components).
The Windows 8 architecture architecture diagram may be useful to see how they relate to XAML / HTML / WinRT. Applications in HTML / JS format are displayed in Internet Explorer 10 Metro, just in a different context (with advanced APIs, various security rules, etc.), while XAML has different mechanisms. WinRT is deep beneath the presentation layer.