Night Hunter vs Invisible Enemies?

Only works if the target is visible per this.

Enemy champions that are not visible to Vayne (through Fog of War, brush, or stealth) will not activate Night Hunter.

Her passive run speed increase only works if the target is visible, in front of her, and within a range of 2000. She does not gain it from invisible units until they become visible, for example she would not gain it until Temoo moves after his stealth while he is in front of her.