I don't think its reluctance to be evil, but wanting a more unique fluff for your general, if it wasn't for bloodlines so many vampires I've read about would be virtually the same.
I for one want a good vampire (not crappy Twilight good though), in terms of him being misunderstood and choosing to fight for good causes. Nowhere in the fluff does it simply say 'vampires are evil', its just a combination of the use of an empire perspective and mostly talking about the bad vampires (I mean c'mon, most of the VC army book is about the Von Carsteins wanting to rule to empire, and when anyone attacks GW's little baby you know they'll be tagged as evil forever)
In the case of my vampire, he'll still feed on humans but that's not exactly his choice, he does what's necessary. He raises the dead and has sired a few gets, again this isn't exactly evil, its needed to give his cause an edge over his foes.
Now consider this, Vlad wanted to rule over the Empire, when ruling Sylvania I'm pretty sure he did improve the lives of the Sylvanians, alot of people in the Empire really aren't that well off (typical neglecting emperors and kings). So, would Vlad have made their lives better (which would have been deemed 'good'), yes alot would get killed for vlad and co to sustain themselves, but then so many more would have died for 'the empire's cause'.
Honestly, I think its easier to say that some vampires choose to be evil, others do somewhat evil things to survive. Instead of saying all vampires are evil, I think they are pushed towards 'evil' by being sired, but some choose not to do evil actions. For example, Abhorash tried to control himself and have others do the same, by choice he wants to be good but he understands that he has no choice over some things (needing blood).
The Blood Dragons seeing need of blood as a weakness does prove my point because THEY SEE IT AS A WEAKNESS, blood is like sex for a vampire so to want to 'cure' that need shows that they are not evil as they are willing to remove what other vampires don't see as a weakness but something to enjoy. In this case they aren't 'good', but they aren't 'evil'. They simply choose like non-vampires do, but have the disadvantage of needing human blood and needing to use the unliving to do what they want because most living things assume that vampires are evil.
In a sense, you could say that the assumptions of the 'good-guys' are what's evil, and this rejection of vampires is what drives them to hate humanity, not because the vampires are evil, but because the humans are ignorant.