If cooperatives can survive and compete with private enterprises without excessive regulation and government coercion that limits and competition and leads to lower productivity that's great. As far as I can tell that's rarely (but probably occasionally) the case unless we're also including "guild" like organizations.

However I'm not sure cooperatives are strictly a "form" of socialism, they have been a part of capitalist societies since pretty much the very beginning. I guess it depends where we draw the lines between partnerships etc. and cooperatives, I guess hiring additional workers who don't have an equal stake/share in the enterprise or subcontracting any sort of labor (let's say on a significantly meaningful scale, but still very hard to avoid) would be it.