In the Johnny Gat introductory trailer, one of his lines is 'Home, Sweet Home'... One of the parts of Gat's back story is that he's FROM Seoul. He's not talking (totally) about the bloodshed, the killing and the ridiculous badassery... He's talking about the fact he's finally back in Korea!
The Boss isn't apparently playable but given the Boss casually changes identities and appearances all the time—who can say they AREN'T?
Johnny Gat is said to be the only survivor of his precinct when he wakes up from his coma. In Saints Row: Gat Out of Hell, Kinzie and Matt's AU selves are shown to be Johnny's coworkers in the Retcon ending, meaning they are probably dead.
Of course that's his precinct in South Korea, Kinzie and Matt were probably from when he was a Cop in the U.S.. Plus Kinzie is Agent Safeword, so she's alive, having ended up in a federal think tank.
