If the XML file will help you displaying data or have control on the fields to display or not, XML is good.
Actually I am doing something close : I made a form with 30 questions and, depending on an XML file, I hide or display those questions (using sections) and even the question is given to me through the XML file.
But be careful, if your XML is subject of changing pretty often, you should not integrate it into your form and only put a link to it.