We should take care when we use elements from the real life. For example in the old Far-West movies the indians, the North American aborigines were the bad guys, but decades later the point of view is different. Adding details of the type "DaVinci Code" may very dangerous.
If your story is in the ancient Israel, you can tell about the periods of moral decline, and a good example is the story of the prophet Hosea and his sinner wife Gomer, but pagans can't defeat Israel but when Yahweh wanted the golden calf whorshipers to be punished. Don't you notice the potential controversies? For example a Irish saying pope Pious V and Joan of Arc could defeat Dracula or other vampire-lord because they are saints, literally, but Henry V of England and Elisabeth I couldn't because they are excommunicated, with a "bad karma".
Or "the vampires are supernatural creatures, they scientific origin is not possible because blood is not enough nutritious comparing with the meat or the carrion, and blood by animals should be enough".
Could I use a picture of X-Pijing instead Christians holy icons to expel jian-shis (Chinese vampire)? Could a vampire to be hurt by water from the source in Lourdes (where Virgin Mary appeared), and from the Ganges river? Could
Hong-Xiuquan be a divine spellcaster in D&D? (No, he couldn't, he was a fool, a false prophet). Could be the corpse of
Muhammad Ahmad be a sacred relic? (No, it couldn't it because today practically no Muslims believes him to be the mahdi).
Other example, you get into troubles if in your story the Muslims are the good guys, fightings against the pagans for the ridda wars, in the time of Abu Bark, the first calipha, destroying the temples of the
Jahiliyyah (age of ignorance, pre-islamic Arabia). Or the DM has Chinese roots, and her story is about the legendary heroes from Chinese mythology helping the characters against the Otoman empire. Here the Turkeys could be angry if they were informed.
Only real religions could be added in your campaign if all factions share the same faith (and players shares a similar point of view about the faith). It is too risky with the antagonist faction follows a different religion. Of course cardenal Richeleu can be the antagonist if you are playing in France XVIII century, but if the villain is a Joseph Smith's disciple, like the victims of
"A Study in Scarlett" the first Serlock Holmes's book (it is not a spoiler if I say the murder wanted vengeance) then the things may be different.