Updated: AWS also has a whitepaper on Creating HIPAA-Compliant Medical Data Applications with AWS [2]. Looks like this is support on the standard non GovCloud stack.
[1] http://aws.amazon.com/about-aws/whats-new/2011/08/16/announc...
[2] http://media.amazonwebservices.com/AWS_HIPAA_Whitepaper_Fina...