The space vampire really felt like an unnecessary add to the entire thing. Could have established similar sci-fi woo-woo with a super-intelligent test-tube baby who might have some lingering trauma from that development.
I don't think that would have fit as strongly thematically. Thematically, vampires being ancient, human hunting predators, who are basically the answer to "what happened if you tried creating maximally anti-social humans", and who "accidentally" got wiped out is just another another round in Watt's repeated hammering home the idea that self-awareness/consciousness is not a pinnacle.
The idea that human kind would in its moments of fear and panic reach back and put an anti-social predator in charge is also thematic. In traditional conceptions of hierarchy of "thinking", we would perhaps imagine the self/meta conscious self as being "the top layer", with the layer represented by vampires perhaps being a lower layer (we would imagine it being above "the reptile brain" though). Yet here, humanity (or human command) has chosen to invert the order. The self-awareness layer is capable and does "let go", because while it loves to take the credit for what the mind actually does, it does in fact understand self preservation (generally), and does understand that sometimes, it just needs to... not really be in control.
Final spoilers - and then there's the extra twist which is that the vampire captain was apparently being puppeted by a computer AI system (also implied to be not self aware) the whole time anyways.
So really, we have a pair of non-self aware intelligent systems probing each other. One deploying scramblers, the other deploying the human crew as end effectors.
The space vampire was fun.
> might have some lingering trauma
Why does every character have to have some trauma? Just because the Oscar committee says so?
I think the space vampire was both a bit of fun (in an otherwise bleak novel), but also one of the explorations of different types of mind/consciousness; the mission has a the narrator (with half a brain), a vampire, a person with 4 consciousnesses residing in one brain, a massively-augmented person, a combat specialist who controls a vast set of external peripherals, and an AI (and, of course, the aliens). They're there to make you consider different aspects of what makes up consciousness.