We absolutely have no idea, Imu can „appear“ on top of his vessels like Saturn and Gunko, but he also can just mind control them, like he did with Gunko the entirety of the arc and he also mind control Saturn.
There was this panel in which we have seen Saturn‘s face (with Imu‘s eyes) when they ordered to sink GV.
So we can assume that Gorosei and HK are Imu‘s vessel, but yet Imu‘s strength can only be shown as Imu himself. It‘s the opposite of Isshiki Otsutsuki