>>534329046
More than likely CA was in need of a big, centerpiece unit and came upon the Incarnates. The fact that Stanky is supposed to be all attuned to the wild probably sealed the deal.

That said, it is fairly faithful to the lore. Human wizards can make pacts or use scrolls of binding to use monsters in battle. Theres a Forge World book that has a story about Tileans and Estalians using Skin Wolves, Manticores, a Warpfire Dragon and Mournguls against each other.
Of course, thats way to many charlemagnes for CA, so we'll probably never see that outside of mods