A little input on vampire happiness - they are sad if their friends die. They can even go stark raving mad.
Also, a vampire who spots another vampire feeding seems to have no problem with reporting the crime correctly (at least 75% of the time)
I had about 3-4 vampires and waaay too many dwarves, about 220. I got declared a barony (my first time since 40d!) and naturally I chose one of the vampires for the position

I had been trying to infect the rest of my purpose using another vampire, some upright spikes, and a well. I kinda messed up: I tried a single tile well, bucket-filled, which should have worked well... except that 10 training spears never pierced his clothes (I guess they're harmless to everyone). I rebuilt it with waaay too many lethal spears, and a multi-tile reservoir, which resulted in water flows which eliminated the blood (it stuck to the walls).
He's still "alive" down there after two hits, and actually quite happy for being underwater with no functioning limbs.
Apparently I didn't fail completely, though - 20 dwarves eventually gained "vampire" status after their profession names. To deal with the other ~200 dwarves, I locked all of my unskilled labor into a small hallway to starve. Occasionally the vampires among them would suck their blood, but I know that that's not necessary. It did help kill off the living though.
ANYWAY to return to my point, my poor baron went Stark Raving Mad in his locked-away office of solitude. He was really attached to his food
The vampires who hung out with the dying dwarves are fine, however. In fact they have between 40,000 and 100,000 happiness! I'm not experienced with this version but isn't that an awful lot? Most of them seem to have made satisfying acquisitions recently, maybe they claimed the clothes of the dying.
One of the happiest, a child with 8562 happiness, had:
Talked with a friend
Made a friend
Lost a friend due to tragedy (probably lots)
Lost an annoying acquaintance to tragedy
Lost a father to tragedy, forced to endure the decay of a father
Lost a mother to tragedy
Lost a sibling to tragedy
Has witnessed death.
Has been haunted by the dead
Disgusted by a miasma (they've all been sitting in miasma)
Took joy in slaughter - this is a mystery to me, as there's no report of him fighting back against the cramped animals in there. Most of the bloodsucking-murders are heavily reported in the justice screen, but eventually they stop (possibly when my Guard Captain went insane) so did he get this thought from sucking blood?
Was comforted by a pet
Admired a very fine trap (not an artifact, no artifacts in there at all)
I know that happy thoughts are notoriously hard to track, so this will probably remain mysterious. I'm wondering if they like to see death though, due to the hates-life tag (whatever it was). Losing friends drove my baron-vampire insane, but something's keeping these other vampires insanely happy. Most of them don't even have pets, just each others company (but they were friends with most of the dwarves who just rotted to death in front of them! Strange!)