The Dawnguard are a elite group of warriors usually born into the fashion that are trained since birth to fight, the main purpose of the guild is to hunt and kill evil Abjurations, fiends, demons/devils, monstrosities undead, Vampires and other such things, and anyone who works with or for them. The guild studies and learns about them so as to be able to hunt them better. The Dawnguard aren't the most known good factions as they tend to keep to themselves as their own society, and only make a presence when the listed things start appearing, the guild consist of lots of humans but they recruit anyone who swears to kill and put an end to those evil things.
They believe almost all non humanoids are monsters and should die, if any of the listed creatures wanted to prove there not it would be very hard
Never work with or trust a monster, if they trick you into being your friend kill them or bring them into Dawnguard to teach them a lesson
Killing the creatures listed above, or getting lost things of the Dawnguard such as their ancient crossbows and bolts made by their founder's artificers before they were lost during a war with the Vampires.
The Dawguard's goal is to kill all, if not that all savages and mutants such as vampires, lycanthropes, aberrations, hive minds, and many other disgusting creatures
The Dawnguard holds the biggest fort in all of Farenguard with some of the best defenses and is self sustaining. The fort holds all knowledge on most monsters and myths and many weapons effective against vampires, lycanthropes, aberrations and the likes.
Together, We accomplish the hunt
The Dawnguard fends for itself and does not need currency, sometimes they trade with other provinces for resources, info, and the such.