And yet they use php? Seems a bit hypocritical 🙂
But anyway, you'll probably find that if your pages are compliant with the w3 consortium's HTML 4.01 or XHTML 1.1 standards, they'll be very very close to 508 anyway, considering for web apps that's what 508 is based on. But AFAIK there isnt anything out there that will test your entire application for validity. I always validate manually, put something in, check it, if it works, yay, try a different thing, then validate that, etc. Takes a bit of extra time, but personally I think it's worth it 😉