As annoyed as I am to agree with you (since I still don't trust the fact that she's a freaking VAMPIRE), you're probably right about Otto being a target for the Hippos (although he IS a resident of Ankh-Morpork, so my earlier theory about foreigners joining the Hippos is still possible).
The ranagrande thing is interesting... although judging from his response, I'd guess that he's some sort of third party. If we're assuming the Hippo League is scum, the normal assumptions of scum/town are in effect. He would have no reason to be bewildered by the thought of a role that didn't involve killing. So if you're right, he's probably a non-Hippo role that still gets some kind of bonus when someone is lynched/killed.
Another post of note: http://www.readandfindout.com/rpg/messageboard/280907/ in which Praziquantel is an apologist for the Hippos. It's not damning on its own, but it's definitely the kind of thing a Hippo would write.
And yeah, how do you know Stephen isn't Hippo League? Did I miss something?