Cloyster is OU, Dodrio is BL/UU, and Jolteon could be both things depending on where you place the cut-off. Anyway, I think all the current OUs are more OU than Jolteon is, but probably Jolteon is also the most common UU in OU right now.
I'm surprised nobody has pointed out Cloyster's explosion yet. It's imo its main selling point over Lapras and to an extent, over Articuno. From my experience, at least 3/4 of the times Cloyster is effectively exploding into a recoverer or a Snorlax unwilling to switch out. Cloyster forces a lot of plays that his explosion is often very difficult to predict.
Clamp is not only useful when you are in a position to clearly sweep, it helps get good matchups and wear down stuff. And in any case, Cloyster only needs Starmie and Alakazam paralyzed to have a chance to sweep. Teams pack one of these two on average, and it's pretty likely that it takes early sleep, a paralysis, Exeggutor's explosion or something, especially in the case of Alakazam.
However, I don't like the idea of comparing Cloy to skarmbliss. The ability to rest loop a paralyzed Snorlax is great, and often slows down your opponent's offense but in RBY, its very predictable when doing this as a rule. Except for a few late-game scenarios, stalling for ever = losing in RBY. A sleeping Pokemon gives Tauros a free turn and that's gamebreaking in RBY. And not only Tauros, but other stuff can also capitalize on a free turn depending on your team and what you have left: Zapdos/Jolteon, Persian, Rhydon/Golem etc. Moreover, when Cloy uses rest, he generally finds unable to wake up healthy enough to make an impact offensively other than with explosion.
That Golem/Rhydon are used only for electrics is not true but I'm unwilling to discuss about it. This is kinda like saying Gengar only exists because Persian and Dragonite do.
Jolteon's advantage over Zapdos is not definitely being able to hit Golem/Rhydon for 10% more damage, which is hardly relevant. Their advantages are being faster than Tauros/Alakazam/Starmie (and thus having a higher %CH), being neutral to ice and resisting electric.
I never saw Gengar or Persian in SPL either, but my experience is only around 1/5 of the total RBY battles anyway. I'm pretty sure someone used Gengar as Jorgen said; 0 Gengars in +40 battles is hard to believe. Regarding Cloyster, I think I "only" saw two, but I used it many times myself. Overall, the usage stats of SPL were very standard, and, at least for me, not really surprising.