A feature was just Added to the VSI with release 4.2.  Just posted to Powerlink.  Access Control Utility is a new part of the VSI framework which allows you to assign specific rights per storage objects of the VNX / CX system. Details are in the release notes.  
I've had this question come up several times:  How do I limit access to Pools & RAID Groups/File Pools from the VSI Plug-in?  Storage Admins do not want Virtual Admins to have access to all storage on the VNX/CX/NS Array.  What is the best method for this?
VSI storage access permissions