I Honestly dont mind getting worse rewards for playing good, As the main reward is knowing that you did a good deed, But we really need some info on the dawnguard faction side, Only info we got so far is that we are grtting armored trolls, The crossbow isnt exclusive and neither is the armor. I hope they tell us more benifits.
unless it's like in morrowind, where vampire hunter clothing would kill vampires trying to wear it!
http://www.uesp.net/wiki/Morrowind:Ano_Vando