You assume that dolphins don’t already have democracy. If wild dogs have it figured out, then it’s certainly possible, even likely, that dolphins do too. Imagine what a pod of dolphins might vote to do with a land mammal that has the audacity to try and teach them democracy.
It mostly makes sense. There are infamous examples of voting being de jure or de facto illegal for groups of people where their suffrage would likely cause significant change. Just look at the USA pre-Civil Rights Act, Rhodesia, Apartheid South Africa, and Israel. I’m sure there are others.