> If I were a small non-union indie shop and I was lucky enough that some highly talented AAA developer wanted to work with me, I would be unable to hire him if he's union unless I converted my entire shop over to be union. If I didn't, he would be in direct violation of his union contract and could be fined or lose his membership.

I've never heard of unions working like this, this may be a US-specific thing. Unions are just workers right groups, if the company is big, the group is inside the company, if it's too small, you just apply to the local union. They help to negotiate better laws and benefits for the whole industry & also directly at a company level in big companies.