Hey I happened to think of this when I was checking some Scout cars this weekend, and just now remembered to check for my self.
The better stainless -- Non-Scout Axles -- are NOT magnetic. With a magnet at check in it would be a quick easy test to check for the stainless axles. That is if the rules only allow Scout Axles. The Scout nails are very magnetic.
Once axles go through the Derbyworx axle straightener and then the head gets the taper, hard to recognize the nail by the head.