I am actually curious what the social politics behind an Octarian being a pop star in this setting are.
Seeing as the single player campaign in 2 still involves you slaughtering every Octarian that casts a shadow, they are still clearly not generally suffered to exist.

You forget no one knows that Octarians exist as a race at all. The Inklings of past completely wiped them to the dregs of society. The only ones who know of the Octarian invasion is Squid Sister, Cap. Cuttlefish and presumably Sheldon. Other than the "Hero" character, no one else is aware of them. So if a gentle DJ Octoling comes out they'll just assume she's one of the other various races of creatures in the world of Splatoon. Until the Octarian invasion is publicized, I think Marina is in safe waters.