OK, primer for everyone on Discworld vampires:

Their basic nature is that of a traditional, Dracula-esque vampire. They turn into bats, suck blood, love billowy opera cloaks and dramatic lightning. They're repelled by running water, holy symbols, etc. If they turn to dust, by say a flash of bright light, they can be reconstituted by dropping some blood onto their ashes.

Now, that said, they're not necessarily evil. There is an ever-growing group called the League of Temperance; this is basically Alcoholics Anonymous, but for blood. Members wear black ribbons, sing songs, have sayings such as "lips that touch ichor shall never touch mine!" etc. Black Ribboners have to deal with cravings for blood, but seem to be able to manage by replacing the obsession with blood with an obsession for something else (like photography, or coffee, or policework). It also helps to have a nice sausage or something around to bite into.

So. There's a possibility you're a foreign vampire (the villains from "Carpe Jugulum," or maybe Sally from "Thud". There's also a possibility that you're an Ankh-Morpork vampire (Otto von Chriek the photographer, or maybe John Smith or his wife of the League of Temperance).

Also, given the way that Isaac did townie/scum with his last game (The Dresden Files), I'd say it's about 50/50 if you're scum or not. Any vampire could have a justified scum role.

And that's ignoring the whole Hippo League thing- one of the chief attributes of a Black Ribboner (a vampire abstaining from blood) is that he becomes obsessive about something else. Even if you're NOT feeding off of us in our beds, there's a decent chance that you're obsessed with killing foreigners.

So, yeah. I won't vote yet, because I want there to be a discussion. But it seems to me that there is a significant chance that Yunalesca is a scum in some form, either by being a member of the Hippo League, or by being a blood-drinking vampire.