Yes, Lovis was soul forged with a stone, and IIRC there is mention of other such instances in books or dialog.
In Damian's case, nobody had ever preformed a soul forge between a living and recently deceased soul before.
Neither Talana or Zandalor offer an explanation of why resurrecting Ygerna will kill Damian. It seems to just be an assumption, based on how regular soul forges work - changing the status of one changes it for the other. That is a reasonable assumption, but lacking any evidence.
