baiscally, raptors in the heresy were used as shock troops, and to attack the weakest part of the enemy line, i.e. the weak spot, like predators. they sort of began to play up to their predatory/elite role by altering their appearence to be more 'bird-like' and they became egotistical predators (like lawyers

). whereas in some stories they are basically just scary looking, jump-packed, marines, in others, like one short story in one of the space marine collections, forget which, and in the night lords series, they are more animalistic, the former dropinng from the sky to attack a load of feral dudes that they keep in fear of them (with one of the raptors looking all daemonic and warped). in the latter, all of the raptors (in blood reaver, void stalker and the short story) are shown as bieng hunched and snarling.
im not sure whether raptors actually worship and particular god or not.
their egotistical nature is why they are outcasts, as most marines see them as prats.
personally i love the raptors, models background and all!!
hope this cures the itch.