Nah Zaniolo is more central. He is mezzala or AMC, while Kulu is RW or AMC.
He doesn't play centrally much, and never mezzala since Fonseca doesn't use them, he is Roma's main right winger.
They play a 4-2-3-1 with a good amount of rotations since Fonseca hasn't figured out his team (and had many injuries), the usual names are
Dezko
Kluivert - Pellegrini - Zaniolo
He is surely young and talented enough to adapt to different roles, but so far he looks best there.
I agree that Kulusevski and Zaniolo would seem to fill the same role in the team. I don't know what Kulusevski will do here though. Maybe Sarri sees him as a midfielder, which I hope for.