Please consider moving this question as-is (no need to recreate) to the proper forum for maximum visibility.  Questions written to the users' own "Discussions" space don't get the same amount of attention and can go unanswered for a long time.  You can do so by selecting "Move" under ACTIONS along the upper-right.  Then search for and select: "Everything VMware At EMC"  Everything VMware At EMC   What you have identified is accurate (ViPR support only for the current v6.0 VSI for vSphere Web Client).  VSI 6.0 for the vSphere Web Client   In the meantime, you'll need to hang onto the native/C# vSphere Client to take advantage of the features offered by the VSI plugins such as USM (Unified Storage Management), SV (Storage Viewer), PM (Path Management), etc.  I simply wanted to also make reference to the following post which has some search strategies (minimize the results) to find the VSI plugins:  What happened to the VSI plugin for vsphere?
I can not find the plugins to provision, expand clone etc.. for the 5.1 vSphere Web Client. The client has plugins but can not find for Web client except for 6.0 and that is for Vipr.
VSI for ESXi 5.1 vSphere Web Client