The conceptual level breaks down in places where an open shop is illegal or disincentivized, which I suspect is the case in California where the Wikimedia Foundation is based. Europe usually has open shops, not closed shops, for example.
No, it doesn't. There is no such thing as an "open shop" in the US, even under right to freeload. Union membership is determined by job classification. If you are working in a unionized environment, and your job title is a union job title, you are in the union. You will be covered by the contract your union bargains with the employer. The only question, then, is whether you pay the dues to cover the costs of union membership. In a right to freeload state, you can choose not to pay the costs.
No, it doesn't. There is no such thing as an "open shop" in the US, even under right to freeload. Union membership is determined by job classification. If you are working in a unionized environment, and your job title is a union job title, you are in the union. You will be covered by the contract your union bargains with the employer. The only question, then, is whether you pay the dues to cover the costs of union membership. In a right to freeload state, you can choose not to pay the costs.