No, a warrior priest is a priest with prayers rather than a spell caster with spells. Spells and prayers work largely the same within the Mordheim game mechanics but there are some subtle differences. Familiars is one of these differences, there are some skills that are only for spell casters (e.g. Sorcery) and priests can wear armour but spell casters cannot. There may be other differences also but these are the ones that come to mind.