For prostate cancer patients with N+ disease, is there evidence demonstrating improved outcomes with the addition of nodal RT, as opposed to prostate RT alone plus ADT?

There is no direct evidence. In the STAMPEDE trial, which showed benefit of RT in node positive patients, RT involved prostate and nodes in a majority of patients (>80%).

I agree with @Dr. First Last that the evidence is indirect. Parker et al. STAMPEDE M1|R0 stratified by N0/N1, noting that those patients also all had metastatic disease.

We 'interpolate' from the evidence for T3-T4N0M0 and T_any N_any M1 that RT to the prostate is worthwhile for N1M0 patients. And we e...