Squirtle situation
I know even hydro cannon Blastoise is useless. That being said, I have an assortment of shiny Squirtles and Wartortles with and without sunglasses. I'm wondering if I should evolve them, or keep ones at different stages. Contrary to what I have read, it's a myth that a pokemon caught during the event gets the exclusive move. Would you evolve any more?
Also, I have a 100% Dragonaire. I know the exclusive move is worse. Again, would you evolve it?

Answers
Reports from Larvitar day were that Ttar raids that caught the bonus afterwards got Ttars with Smack Down. IMO this would be one of the huge benefits of the Community Weekend - do a Ttar raid, and get a SD Ttar at level 20 (or 25) with an IV floor of 10. No spending 125 candy to evolve the Larvitar, just power it up and you're done.
What is your source for the exclusive move not applying to caught pokemon? The usual language in the CD announcement is 'any {Tyranitar} caught or evolved during the community day will have the exclusive move.'
Regarding the dragonair you can TM the move at any time for Outrage. I would only evolve a lesser IV Dratini for collection purposes only, but those 125 candies are better spent powering up more Dragonites.
Fully evolved pokemon caught during the event window indeed knew the exclusive moves so you should definitively check some Ttar raids (although this being a longer time window that may no longer apply)
I'll say this regarding that Blastoise above, you either:
- Evolved it outside the CD window
- Lost GPS when evolving, which means it won't get the CD move (Happened to one of my fiancee's 96% Metagross. Luckily trades got her a lucky 96% and lucky 98% to make up for it)
Tyranitar caught from raids on Larvitar Day knew Smack Down; I caught one myself. While I don't have a link, supposedly someone on TSR caught a wild Charizard on Charmander day that knew Blast Burn.
About whether to evolve or not, that's up to you. Do you want various stages for collection purposes? Do you want to have extra Pokemon with the CD move for trade bait in the future? If not for the CD move, what else are you saving them for?
The Dragonair depends on how badly you value keeping less than optimal moves for novelty. Draco Meteor - while still usable on Dragonite - is worse than Outrage. If you want it to be the best of the best then evolving it outside the CD weekend saves you a charge TM.