
I think, just my pure assumption, that Dawnguard, the faction that uses a "rising sun" emblem and who are obviously vampire killers for sure, aren't concentrating on other undead, werewolves and daedroth, like Vigilants.
I've always thought of them(DG) that they're a specialised vampire-hunting-oriented former VoS.
It's also based on 2 things(characters/bodies to be precise) I've spotted:
1.DLC Trailer : We see a dead shirtless body of the Vigilant of Stendarr(boots/ amulet of Stendarr)
2.e3 Gameplay: We see a Vigilant of Stendarr(higher ranking one) wearing an Vigilant Tyrrus robe(Adept Restoration Robe?) who's talking with "DG leader"...And you can barely hear that they're speaking of "vampire attacks increased" etc.
So they either have close relations with VoS in business way, sort of specialised work(vamp-hunt-exlusive elite warriors)
OR
They're "child-organisation" with VoS being it's "parent-organisation", that parted ways with VoS due to their will to specialise[vampire-hunting] rather than fight with "the whole myriad of evil blaphsemous creatures of Hell, that Our Lord Stendarr hates".
Opinions?

Also: I don't think they are followers of any daedric deity or Werebears(too-Companions-like). They're just Vamp-hunters. I could be wrong of course:D

