Havroun Weibe and Krait
I think it has nothing to do with the Raven spirit. The Havroun are powerful Norn shamans, able to pass through The Mists – and Havroun Weibe is an exceptional Necromancer amongst them.
To amplify his knowledge, he early began to dedicate himself to areas of unholy and profane magic which most Necromancers wouldn’t step a foot into. By now, he is one of the strongest Necromancers in Tyria.
It certainly is one of his preferences to summon Krait as minions from the Mists. It has nothing to do with the Raven – it must be Havroun Weibe’s personal fascination for the Krait. By the way, the Krait have a completely different “religion”, and the Krait see themselves above other races. There wouldn’t be any reason for them to get some connection to “lesser” Norn spirits. They might even see every other belief as false and impious.