<p>Anyone know uf there's a dll/runner anywhere that returns TAP output from an NUnit test suite?</p>

Seems unlikely to me, since there is an impedance mismatch. TAP has no concept for what NUnit calls a test, and what TAP calls a test usually corresponds to an NUnit assertion, but not precisely. So I’m not sure how the thing you’re looking for would work at all. (But maybe a heuristic could work well enough.)