Is he a fanatic? His VO is about finishing what he started, which should be a reference his dead daughter and the Dark Justiciar War, but we also know that Ketheric tried to get the Sharrans at Grymforge to worship him over Shar, a blasphemy. As far as I know, nothing from the Moonrise curse has anything to do with Mind-Flayers or the Absolute, which appears to be fairly recent. Not that they aren't connected.
Also like you said, if Shadowheart is working for the Sharran's then Shar and the Absolute are at odds.
