VMware vSphere 4.1 has been awarded IPv6Ready Logo 02-C-000488 for IPv6 RFC compliance.
IPv6Ready Logo certification is particularly interesting because it is the generally-accepted standard for IPv6 RFC compliance, recognized around the world. NIST certification is applicable to the civilian U.S. Government.
For more information you can read Milin Desai's recent blog post on this topic or visti the UNH site for USGv6.