vSphere supports IPv6 for all major traffic types (guest Oss, management and VMkernel e.g. IP based Storage)

New in vSphere 5.5
- TCP Checksum Offload: For Network Interface Cards (NICs) that support this feature, the computation of the TCP checksum of the IPv6 packet is offloaded to the NIC.
- Software Large Receive Offload (LRO): LRO is a technique of aggregating multiple incoming packets from a single stream into a larger buffer before they are passed higher up the networking stack, thus reducing the number of packets that have to be processed and saving CPU. Many NICs do not support LRO for IPv6 packets in hardware. For such NICs, LRO has been implemented in the vSphere network stack.
- Zero-Copy Receive: This feature prevents an unnecessary copy from the packet frame to a memory space in the vSphere network stack. Instead, the frame is processed directly.
vSphere 5.1 offers the same features, but only for IPv4. So, in vSphere 5.1, services such as vMotion, NFS, and Fault Tolerance had lower bandwidth in IPv6 networks when compared to IPv4 networks. vSphere 5.5 solves that problem-it delivers similar performance over both IPv4 and IPv6 networks.
Source: http://bit.ly/16SqiVU