Is possible for dashboard OSX widget to be installed on iPhone ?

Nope. At least I am fairly certain.

 

Could all the code be loaded by a UIWebView, perhaps? It was my understanding that widgets were written using JS, HTML, and CSS, not unlike websites?

 

That's what I always thought. Someone please confirm it.

I am actually planning to do something like this: embedding a widget in a WebView as a menu bar app on the Mac.

 

Try it and let us know how it turns out.

(Same goes for the OP...)

 

It works Here's a demo project (Mac).