Chances are slim that Stephen talked to F-T about his role because Isaac stated that Stephen was 'critically inactive'. However, this info could've been in F-T's role message when they were in the same (mason) group.
I'm also still trying to get the picture of what this game is about. We obviously have a group that hates foreigners that kill and attack with a sense of humour (a dwarf from ramptop mountains killed with a battering ram, a teethbrush seller with a sack of 'teeth', a dwarven diner attacked with battle bread). The attack on Stephen seems a bit out of line here. Of course Sally is a vampire (wich should be enough reason for the hippo's to attack), but in the method (looks indeed like hogfathers' sledge)I can't see anything that points to either vampires or überwald.
Besides the hippo's we have one other vampire confirmed (yuna) and a wizard confirmed (rana). I don't know if that's enough to supsect a undead group with nighttalk ability, although I wouldn't rule it out. IMO it's also entirely possible that we have a City Watch-group in this game too.