The Nimble Plugin for VMware Web Client is natively integrated into the Web Client and embedded into the VMware functionality. There is a really great blog (link below) that details the capability of the Web Client.
With the selection of initiator groups and performance policies this is not yet implemented into the web client, but is something we do automatically today. The vSphere 5 Performance Policy is automatically selected when provisioning a datastore, and we automatically detect if an initiator group exists for the selected hosts, if not we create one.
Unfortunately I don't know if this is something we are looking to change in the future.
Hope this helps.