Apple - How to view Silverlight traffic in Safari Web Developer?
I can't understand if your app do a XmlHTTPRequest.
Anyway... in the resource section (red circle in the image) you can find all the information about a request, even its response.
Hope this will help you! :)
PS: Sorry, my GUI is in italian, but you will understand as well
If you click on Network Requests (in recording mode) you will see list of all request in the table. If you select a row it is highlighted in the resource section. Clicking on it will show its body.