Well actually the data I use to determinate if a proxy is within a network that is partly or fully controlled by spy agencies is a bit outdated. You can safely say that almost everything is under there control. However if something is run by them directly, it's of course questionable if you should use it for sensitive tasks.
If it comes to SEO then I don't think they are interested in that data anyway. For us SEO guys this is not that relevant. I however would not use that kind of proxies (as probably all public once) for gray activities.