Is Jin Sakai's Ghost legend referenced in Ghost of Yotei?
Yes, but very subtly and in a way that feels organic. The legend of "the Ghost" has spread beyond Tsushima in the century since the events of the first game, but it's become a kind of folktale or myth. You might overhear travelers in a tavern telling a distorted version of the story, or find a collectible scroll that references a "shadow who fought with no honor to save his people." It's never a major plot point, but it's a cool piece of world-building for fans that establishes that Jin's actions had lasting consequences and entered the popular imagination. It's a nice, quiet nod, not a heavy-handed reference.
I've only found one direct reference so far, and it was in a side quest where an old monk mentions a "legendary warrior from Tsushima island who communed with the wind." It was a really nice, understated Easter egg that made me smile. They definitely don't beat you over the head with it, which I appreciate. The game is confident enough to let its own story and legend take center stage.