brinnel hardness of tool steels are in the 600-900 range.. nickel is in the 100 range.
If you actually read that redding info page, you will notice that the nickel is not SCRATCHING the die, but may be sticking to the inside of the die, and scratching the brass run thru it..same way that brass chips can stick in a die and then GALL the next piece.
This goes back to my initial comment.
dirty dies and sticking dirty cases in. the redding article backs this up. You stick in dirty brass into your dies, you get junk stuck or embeded into your dies.
Hornady was not at fault here.. the reloader with bad cleaning etiquette was at fault.