Yes, but that's very different - the Eurozone countries are not allowing another nation's currency to become their defacto currency, they're creating a pooled economy where they all still have a voice in the management of the common currency. (And it's still causing a ton of problems, when you consider what's happened in Spain, Italy and Greece.)

It's radically different from allowing your defacto currency to be one managed by another country, particuarly one that has no common economic interest with yours.