Profiles are crawled periodically and are also checked for 301/404 status code, if a 301 or 404 is discovered, the profile is considered deleted and the videos will be removed.
The crawlers obey the robots.txt by checking for general rules and for its own signature. Should they not find their own signature, they fall back to checking for rules for googlebot.
The bot uses an user agent that can be associated with us and is conform to other crawler user agents.
Reverse dns validating is as of now not possible.