8th Ed. How to Skink Chief - or "Why should I bother?"

From page 105: "Ridden Monsters and Special Rules
We assume that special rules that apply to a ridden monster do not normally also apply to the character riding it and vice versa"

Even if you make the argument that the wording of Unstoppable Stampede supersedes this, Devastating Charge reads that "Models with this rule have +1 Attack during a turn in which they charge into combat." So IF the entire model gets Devastating Charge THEN the entire model gains exactly one extra attack on the charge. Best case scenario for this interpretation of the rules might allow you to give that +1 Attack to the Chief INSTEAD of the Stegadon.

But I don't think it passes the smell test, personally.

 

That's fair enough Works for me, plus the Steg would have a better attack than the rider could muster!