No - the code will not execute. What you're describing is an "injection" and, if it were possible, could wreak havoc in an app.
Something I've done in the past is create an app with a UIWebView container (somewhat like you're describing) then pass back a response that my code can programmatically look for and handle. This is of course possible by the fact I wrote both the app and the web back-end.
I'm sure there are other ways to do this but it has worked for me.