Worker co-ops are quite concretely socialist in the sense that the workers control their means of production. Of course when embedded in largely capitalist economy, e.g. banks do still have often de-facto control over them.
Or you could say that they are co-owner of their means of production. So, as business owners, are they actually the ultimate capitalists in disguise? :-)
Business owner who doesn't have employees is not really a capitalist, but a self-employed worker. At least if they do some practical labor instead of e.g. investing.
In general, self-employment is quite a different thing from owning of means of production that other people work.
Or you could say that they are co-owner of their means of production. So, as business owners, are they actually the ultimate capitalists in disguise? :-)