I asked WA Support about this very subject back in August 2008 and their answer was
Validation Toolkit does not support form elements that include a dynamic from elements name, because the Validation tool kit will insert code that validate form elements using the form element name. 
I ended up using a JS solution as this was part of a multiple add to cart routine that I was working on which you can see in action here: image.php?name=is-it-a-sine&id=46


