In fact, there were many saints VIDAL in Italy, France and Spain. For example, the first Salsburg's archbishop was called VIDAL and came from Italy (Ravenna). Moreover, a seigneur's family from Velay (Haute-Loire department in France)was called de la Tour de Saint Vidal untill 16th century. They owned Saint Vidal's castle which still exists in Saint-Vidal village. At last, there could be a jewish origin during crusades. Some converted Jews could come in latin countries with catholic seigneurs as de la Tour de Saint Vidal and, by pun with King David and vita (life in latin language)could take the name of Vidal. Is-it true ? I don't know. Amicalement.