They did say that Kazekage (Sand's Kage) + other sand villagers were afraid of Gaara. Kankaru said he lost his appetitate when he first saw the monster when he was around 6 ? So that means the villages + kazekage must've known about the monster in Gaara as well, and thats why they fear him.

No, I dont think the monster is Jounin-level if Kagekaze fears it. Probably at least hokage-level or sennin level