It's the same as what happens with Austria's Diplomatic Marriage, right? Except that where Austria allows the city-state to at least retain the dignity of an alliance through marriage and maybe even a Dual Monarchy, Enrico just buys them out like an evil CEO doing M&A.
Venice: soo, we give you all this money, and you join us ok?
City state: but uh, we kinda want to stay independent, and we can make own own Monearghh!
Venice: (hits mayor on head with money bags) ok, anyone else got any objections? no? lets do this!