Yes You can but not in single player if you get the Multiplayer Legends And killers you can play as red dead revolver characters online. but not for singleplayer and lairs and cheats and undead...
R.D.R undead nightmare is out now as a standalone disc.Sharkboy67: Also, you can buy a disc that has it and red dead redemption on it, or you can go onto the game marketplace and buy it for 800...
No, if you buy the one for 20 dollars that is undead nightmare but not the original. The only way to get both is buy the Original Red Dead Redemption and then buy the Undead Nightmare add-on