This post will be a useful guide for the Red Dead community or anyone interested in this topic. Many are the players who still, to this day, generally believe that the Red Dead franchise has only 1 universe, unlike the main Rockstar Games franchise which is officially made up of 3 continuities and these ultimately interconnect with titles from other franchises also developed by them.
Like the Grand Theft Auto series, the Red Dead series is divided into three self-contained universes, as Dan Houser (Vice President of Rockstar Games) confirmed that the events of Red Dead Revolver take place in a different canon, and its events are treated as legends and myths in the Redemption continuity (Red Dead Online, Red Dead Redemption 2, and Red Dead Redemption canon) Undead Nightmare is set in a parallel universe and is not canon to the Redemption continuity.
So if it's not canon, why do the campers in both Red Dead 1 and Red Dead 2 mention characters and events exclusive to the narrative of Red Dead Revolver? Does it mean Rockstar contradicted themselves or that said events also happened in this continuity? The answer is no.
You see... campsites aren't exactly reliable sources of information. In a gameplay trailer for the game, and this can be verified, a narrator states that players can join random NPCs at campsites and hear news and rumors of the Western Frontier when describing their functionality. Some NPCs talk about hidden treasures that the player can actually find, but others boast about mythical characters and events they believe to be true, stories that are full of exaggerations.
Now answering the initial questions again: NO! Red Dead Revolver falls under the category of folklore in this universe and nothing more.
The topic of Undead Nightmare being a dream sequence scenario of John's all along has already been debunked by the screenshots shown above, plus the DLC is also referenced in GTA 5 and Red Dead 2 so further discussing this is pointless in my opinion. And it was always a fan theory, not something suggested by the company itself.
Next common dilemma:
Why do people find it difficult to understand the concept of different universes in the franchise? Actually, both parties are to blame, the company and players: the first group for not directly answering these type of questions on the company's official Twitter account and the other group for not doing enough research. We have to keep in mind that there are casual gamers and fans, we can't expect casual gamers to spend a lot of time googling information almost 24/7 about a game company, the same can be applied to content creators. It's not common knowledge out there, but among the fan community it's a well known fact that the Red Dead franchise has 3 universes.
Explanation for casuals:
In the movie Multiverse of Madness we see the Planet Volmir and Thanos with the gauntlet but instead of the "Avengers" being present in that battle we see "The Illuminati", a society of supers made up of Reed Richards, Professor Charles Xavier, Black Bolt, Baron Mordo the "Sorcerer Supreme", Agent Carter, and Captain Marvel (Maria Rambeau). The battle at Volmir in this universe, known as "838", is based on Avengers: Endgame but it occurred differently.
Explanation for fans, but only for those who deny the Rockstar Multiverse because their IQs equal the room temperature in an igloo:
The Call of Duty franchise is divided into not 2, nor 3, but 5 separate universes. This is due to the fact that 3 developers have taken over the franchise throughout the years. In Modern Warfare (the reboot) Captain Price says the line "On your feet, soldier! We're leaving." which is a nod to the Captain Price from Call of Duty 4, and this version of the character also claims to have shot Zakhaev, something that also happened slightly different in Call of Duty 4. And both characters have different ages.
Red Dead Revolver was originally a Capcom project, then it was bought, finished and published by Rockstar Games, but Rockstar eventually decided that they should further expand this recently acquired franchise and thus Red Dead Redemption was created around 2005-2006, which is a reboot/spiritual-successor of Red Dead Revolver. Undead Nightmare, on the other hand, was developed by the same company, but it was a different approach that certainly wouldn't fit into the serious and dark GTA 4-like narrative seen in Red Dead Redemption, so they made it a standalone zombie title filled with lot of fan service, that is also inspired by the Zombie genre of the 1970s, and that is not part of any canon or universe.
I hope my point of view better exemplifies how these universes work and the reasoning behind Rockstar's decision to separate Red Dead Revolver, Red Dead Redemption, and Undead Nightmare, narratively speaking.
