For once I'm rather split on an issue involving our beloved game industry. For one, a simple red cross as many have pointed out seems like a very basic symbol, and while it is protected and not copyrighted, it seems like it would take a very long time to get rid of all the infractions.
However, that being said, it seems to me the whole purpose of the Geneva Convention's rules on the use of the red cross emblem was to make it easy for those really in combat zones to seek medical aid. Just look for the big red plus and you'll be A-OK.
Think of an example that was mentioned in the interview: people using the red cross for their computer repair companies. In a theoretical combat zone, someone is wounded and looking for medical attention. They see the red cross and think, "Ah! Medical help!" only to realize it's a computer repair company.
That being said, games aren't real life. And to sum this all up, I'd say using the caduceus would be acceptable. I know at least in my local area, the caduceus is used in EMS, such as on uniforms and ambulances: http://www.sunstarems.com/images/homepix.jpg