The Hashishin were Nizaris, the Fatimids weren't - the Nizaris killed both al-Afdal Shahanshah, after whose death the Egyptian government collapsed and the last 'real' Caliph nine years later. Yes, most of their murders were against Sunnites, primarily due to geographical location.

Yes, I know you said 'perhaps' but I was just clarifying. I've done a lot of research on this for 12th Century Glory (in the sig.).