This will effect the validation. Since it depends on Session variables for storing validation information and I don't think php and ASP sessions can communicate with eachother.
You can probably get the validation to work, but you won't be able to repopulate the form with the validated values on failure. You might be able to get around that by using WebAssist cookies toolkit and storing and retrieving the form from a cookie.
The validation code has to be applied on the form action page. So you would apply it on the thank you page.