Well I am not saying you cant do that. Although I have never heard that before!!
As a trained taxidermist of some 38 years you need to fix a skin first prior to tanning. Using any salt or Alum is NOT tanning it is curing, and diesel is fixing a skin not tanning.
All I will say is that if I tanned skins for taxidermy purposes or for rugs in such a manner it would ruin them and make them unfit. If you are tanning for a rug you need a chrome tan, if you are tanning for taxidermy you need Lutan FN. There are many tans on the market but very few are used in taxidermy work, and for rugs you need a tan that produces a denser pelage. If you end up using Alum it will be like a piece of sheet metal, and will reabsorb moisture from the surroundings and one wet salt loving bacteria can make it rot and slip.