No, Assassins Creed Shadows' Yasuke isn't an assassin, and yes, that does mean he won't play the same way the series' protagonists traditionally have

Yasuke, co-protagonist of the upcoming Assassin’s Creed Shadows, is not one of the titular assassins, which means that he’ll play a bit different than you’re used to.

“Yasuke is not an assassin, because the narrative makes sense that he is not,” Lemay-Comtois said.

For the most part across the Assassin’s Creed series you do, in fact, play as an assassin, but there are occasions where you don’t even if they’re few and far between.