In modern generations there are just a lot more "things to do", which creates roles. In RBY, there are basically only 3 real things you can do: spread status, make offensive progress, or wall an enemy from making progress.
Spreading status is fairly elementary - broadly speaking, Sleep is very powerful and Paralysis is also quite good.
Making offensive progress and walling enemies is all relative: you're good at it depending on how you match up with enemy pokemon.
So it's a bit useless to think of it in terms of stable roles: sometimes your Zapdos is queueing into a Rhydon/Golem and its role is... at best luring them on the field so that you can double on them, or just being sacked for tempo. Sometimes it's queueing into Jolteon and then it's usually best to use it to push Paralysis on it so that your other pokemon can pressure the Jolteon more (since they match up with it so much better). Sometimes it's queueing into none of these things and it can be a nasty wallbreaker, or an agility sweeper even. But both of these things are essentially just "this pokemon beats the enemy pokemon 1 on 1 and nothing else switches on it for free, so it gets a concrete advantage".
Even other RBY tiers tend to have slightly more elaborate roles - Amnesia and Swords Dance users are much more viable across the board, so the concept of a Sweeper (ie. something that doesn't naturally beat things 1 on 1, but can with a free turn or two) is relevant. None of those are really much good in OU beyond the occasional Slowbro.
So understanding a game of RBY does not go through "roles" in the ways newer generations do. It's all about parsing the matrix of how each of your 6 pokemon matches up to the enemy 6 - identifying which pokemon will make the most progress most reliably, which ones you need to hold back because they're your only answer to something on the enemy team etc.
You can build some heuristics for that - generally Tauros is good to save for later because it has a great match up spread into most pokemon in the tier and can finish things off with his high speed and Hyper Beam, while Chansey is hard to displace and therefore good at early game status spread, and Snorlax is great but slow, so he thrives as soon as paralysis support is in place to flip a few of his match ups from "loses because slower" to "wins because faster".
But these are loose concepts that will not be true every game. Mastery of RBY is built by understanding how the greater picture changes based on different pokemon, different moves etc. from game to game. And of course, doing all of this through the fog of no information on the enemy team on turn 0.
In summary: no there are no "roles" in RBY OU the way you have them in modern singles generations, and especially not in the way you have them in Doubles formats where entire playstyle-defining moves exist (speed control, fake out etc)