That's an interesting idea, but there is a slight difference in tone between Deus Vult and Gothic Horror / Dark Fantasy.
(EDIT: Having a second thought, you might be able to get away with this if the Reformation fractures the Order. Perhaps a Protestant splinter group pursues adopts Calvinist theology and pursues supernatural evil from within the Puritan community while the main body of the Order remains within the Catholic Church and gets quite chummy with the Inquisition. The Protestant splinter group are regarded as heretics by most members of the order, but has had some spectacular successes confronting ancient evils directly. On the other hand, the protestant faction has become deeply embroiled in the politics of England and the Netherlands - their open support for the Covenanters amongst Scottish Presbyterian community led to persecution under Oliver Cromwell. Meanwhile, the main body of the order became embroiled in the witch-hunts sweeping the continent....)