To my knowledge, there isn't a good up-to-date list of all gym defenders with all movesets.
You can probably figure it out for yourself by looking at the move details on this site. For example, Dragon Breath:
https://pokemongo.gamepress.gg/pokemon-move/dragon-breath
You can see that the "Defensive Damage Per Second" is 2.4, which is the same for Water Gun.
Given that Dragonite has higher base attack than Vaporeon, you can assume that Dragonite would do more defensive DPS with Dragon Breath than Vaporeon would do with Water Gun.
However, you'd need to consider other factors. Vaporeon has higher base HP, and doesn't have a double weakness (while Dragonite does). On the other hand, Dragonite has higher max CP. You'd also need to consider their charge move.
