Did Ornn Craft Yorick's Spade?

I don't think so personally.

Ornn threw the spade to the west, while the Blessed Isles are to the South-East of the Freljord. It's not impossible that the Spade somehow ended up in the Isles (they collected magic artefacts afterall), but it does punch a hole in the theory. It's all possible that the unnamed storyteller is simply wrong about this fact. It is an ancient tale afterall; it's not necessarily all true.

Also, Yorick's spade seems sort of boring for it to be an ancient tool of a demigod. All the other monks used spades as well, and there is no mention in the lore of Yorick's being different. It also has no obvious magical properties: all of Yorick's abilities can be explained by the Mist and the vial of holy water he carries.

My guess is that Ornn's spade has not yet surfaced in the lore. Perhaps it will be the tool of an upcoming champion, or a new item. Maybe it will appear in the lore somewhere but not make it into the game.