I can only speak about Keynote for Mac as I dont have an iPad and cant test it for you.
You cant embed a live webpage in Keynote for Mac, but you can create a link which will launch the default web browser.
Create a button by placing an object on the slide;
in the Inspector > Hyperlink tab > enable hyperlink > link to Webpage > type in the URL
when you play the show, clicking on the button will launch the web browser on the page you have fed in.
Give it a try and see if it carries over to iOS.