I am absolutely not a lawyer, but I wouldn't do something like this for fear of falling afoul of anti-obscenity laws. For instance, the UK has a cyberflashing law which allots a two year custodial sentence for sending a graphic image (by any means) with intent to cause distress.
OTOH, people accessing the game through iframes may be in breach of the computer misuse act for unauthorised access to content.
Then again, I doubt someone is going to file a police report, especially when the URL of the page would bring the reports to an entirely different web page in the first place.