I'm pretty sure he doesn't have the Sharingan despite his use of fire ninjutsu, genjutsu, and red eyes (Kurenai also has red eyes) But that being said I have reason to believe that he may actually be related to Mui, from the Naruto & the Blood Prison movie, in some way. As Mui is the only seen user of Fire Style: Celestial Prison, a similarly unique move that Scarlet Blaze ALSO has access to. And it's been stated that the technique was developed by Mui's clan. So it's possible that Scarlet, for some reason or another, lives & works in Konoha as opposed to Kusagakure. Maybe the opportunities for being a ninja are just better? Anyway, those are just my thoughts on the matter.