As it stands, getting a Kingdom from a Crusade makes you independent no matter what. I had a vassal king of Brittany who was the beneficiary of a Crusade for Jerusalem (he had a claim as the grandson of the First Crusade beneficiary, retaking it) and Brittany and its random assortment of vassals' held counties throughout my empire went independent with him. Was a giant mess, though my vassals cleaned that up in a hurry... basically all of them declared de jure or border dispute wars on him instantly and took all his non-Jerusalem land in moments.
I think it's an unintended consequence of the usual (intended) independence of Crusader Kingdoms, but who knows, they make think it's working as designed