But it's a grab...that sends you downwards. o_OTechnically the defenition of spike was describing a move that had a hit direction that sends you downward. Ganon's is more of a grab, like bowsersides. Ganon can stomp anyways - who doesn't want to stomp?.
So by your posted definition...it's a spike.
???
I know he can stomp, it's not like Ganondorf is going to side-b into the ledge as an edgeguarding tactic.
But this is for the sake of knowledge. ._.