Really curious on why there is no Risen Karkas or any evidence that Risen placed foot on there. They were in the way between Claw Island and Orr.
Canonically, yes the Lost Shores weekend and lead-up was set after the events of the Guild Wars 2 personal story and the defeat of Zhaitan, so this is partially what made it possible for the karka to establish a clawhold on Southsun Cove.
As to whether there can be risen karka: while it’s not entirely out of the realm of possibility (although pitting dragon corruption vs. karka impenetrable shell would be an experiment I would be interested to watch), the karka are recent arrivals to the surface from their original home deep in the ocean. The ocean is a big enough place that the karka managed to settle on Southsun without encountering many risen, and they avoided Orr for the same reasons they fled their home. The karka are an old, old species so they have encountered Elder Dragons and their minions before…and they’re certainly smart enough to understand the threat they represent.