Size > 2 cm, PNI, poorly-differentiated histology are the three main negative prognostic factors, assuming widely clear margins, so he certainly has one of them. If the dermatologist/surgeon said they would be able to re-resect if it recurred, I'd be more comfortable observing. If the re-resection would be technically difficult or compromise function, then considering postop RT might make sense.
How deep was it? Path showing negative margins is usually just that, but if it was involving or near an important structure that is hard to resect like vessel, muscle, nerve, or bone, sometimes that would push you to give radiation or go back for surgery to ensure any questionable areas are resected. If the surgeon is reliable, they should be able to tell you if they suspect any residual for whatever reason.
ya close obs in this case would be reasonable particularly given presumed low grade; he has 1 high risk feature of size but that size is quite large. How did it get this large? May be concerned about a guy like this following up if that is the situation which would be another risk factor. The main thing w skin (our whole field really) is that you are trying to assign a risk of recurrence and think how much you can reduce that risk.