I dug up my Third rulebook. p.327: "The Divine Realm is the manifestation of the supernatural power of the Church and all with faith in the One True Deity. All other powers not of the Church are unholy, and considered aligned with the Devil and the forces of Hell." p.294 treats Constantinople, let alone Palestine, as a place of legend.
While that doesn't name Islam, it seems pretty clear cut that it's opposed to the Dominion (as are all pagan gods). It reads to me like someone trying to describe the (Western Europe) mediaeval worldview without being too offensive.