The VMware implementation of the API has not shipped yet. Each service provider can decide whether they want to provide their own implementation of the API or whether to use the VMware implementation when it comes out. Since the VMware implementation is not out yet, if the vendors you've listed provide the API then they probably wrote their own implementations.
The current 0.8 draft spec does not include performance related statistics around the operation of VMs such as CPU, Memory, Disk, and Network; these may be added in the future. If you'd like to find out more about integrating your existing virtualized infrastructure into these cloud resources please feel free to reach out and I can provide some more information to you.
VP of Engineering, Reflex Systems
http://blog.reflexsystems.com/2009/08/17/iaas-cloud-drift/ <- This is a blog post that talks about seamlessly moving VM's back and forth between your enterprise and vCloud based service providers.