"Any copying, aggregation, display, distribution, performance or derivative use of craigslist or any content posted on craigslist whether done directly or through intermediaries (including but not limited to by means of spiders, robots, crawlers, scrapers, framing, iframes or RSS feeds) is prohibited"
I think this covers Google cache or any other method of gathering data. You're still in violation of their Terms of Use even if you find a clever means of getting around it.
Simply because it exists in the ToS doesn't mean it is legally enforceable. Hopefully the "legally kosher" claim means he had a lawyer look over everything, and conclude that clause in the ToS is for the courts to decide.
I think this covers Google cache or any other method of gathering data. You're still in violation of their Terms of Use even if you find a clever means of getting around it.