Doctors can protect any one player of their choosing. Some mods will not allow a doctor to protect themselves, because it'd be pretty tricky operating on yourself, right? So yes, they can be night killed.
Hiders pick somebody to hide behind. If the hider is targeted, the person they are hiding behind dies instead. If the hider's pick is targeted, both players died. So most likely, Yosuke chose to hide behind Dojima, and Dojima was targeted by a killing role, most likely the mafia, killing them both.