Thanks for your response, Philip. My research indicates that a 301 redirect on a location that is being reverse proxied would result in an infinite loop. (source) I haven't tested it to confirm, though. Is that true?

Since the subdomain does still exist live, someone doing a reverse proxy would need to take some steps to mitigate duplicate content issues. The first would be to set up the new permalinks and rel canonical tags via Wordpress and Yoast's SEO plugin (which rocks, btw). Then you would need to do the robots.txt/GWT steps that you quoted. If there's anything else that needs doing, I am definitely all ears before I attempt this.