I'd say only to soulcaster savantism since it's linked to the essence they soulcast with whereas allomantic savantism is linked to the ability the metal grants.
As for pulling into the cognitive realm, we know regular soulcasting requires interaction with the c-realm and from the description of her soulcasting the stone she enters it like a nahel-bonded soulcaster. When anticipationspren appeared around the captain she said she saw something else so perhaps soulcasting savantism does indeed blur those lines, seeing both p-realm and c-realm layered over each other.