Well, if you've designed your application properly, you won't have scads of logic inside the UI anyway. It makes much more sense to separate the actual work getting done into units separate from the UI, and then test those.
If you do that, then the only code in the UI will be code that invokes the backend, so simply testing the backend is sufficient.
I have used NUnit ASP in the past (at my job), and if you insist on unit testing your UI, I would strongly advise you to use ANYTHING but NUnit ASP. It's a pain to work with, and tests tend to be invalidated (needing to be revised) after even the most minor UI changes (even if the subjects of the tests don't actually change).
