Even though VMM 2008 R2 (beta or RC) does not officially support VMware vSphere/VI4, we have a few customers that have gotten some of the functionality to work.
However, one of the issues that can arise is a failure to find paths in ESX storage. Typically, a VM refresh (refresh-vm cmdlet) might fail with error 2903 - VMM would not locate the specified file [datastoreXXX]\...\...vmdk on the <vmware server name>.
In some cases of creating a new Virtual Machine on an ESX server, the VMM Job could fail with error VMTargetPathNotFound (617) - Virtual Machine Manager cannot find or cannot access the location [storageXX (XXX)]\ specified for the virtual machine.
To correct these issues, a workaround exists. Simply restart the VirtualCenter service which will refresh the datastore and allow these paths to be found by VMM.
Stay tuned for updates on the supportability of vSphere on the SCVMM team blog.