Can I create surveys with unique URLs for each recipient?
You can use the webform API in a tiny module to access the form to add a hidden element to it. Then use the handy Drupal arg() function to determine the value of your unique URL argument. After, use the webform API function to change values before saving to the hidden field for administration usage later.

I can't guarantee this will work so hopefully some of the other Drupal Stack Exchange folks can verify this.