"...full strength with like materials..." That's the problem, isn't it? They are not like materials. The spinner nut is aluminum and the prop shaft is steel. I wouldn't trust just an aluminum nut on a a steel shaft.
I had this problem on my RCV 60 SP. It comes with the split jam nut. I wanted a spinner nut, partly for looks and partly for the starter. I might have tried the spinner nut over the steel nut, and not used the split nut, but thread space was marginal, so I used the stock set up.
The starter works fine without the spinner nut (RCV provides a separate shaft for converting the start to a heli-like starter, but for the 60 SP starting from the front is fine).
Jim