VSM does not work with Linked mode vCenters so that one VSM would be able to access two vCenters. You will need to deploy two VSMs.  You can't run both VSM 3.5.x and 4.0.x at the same time.  
I have SanHQ and HIT running well on vSphere 4.1. After upgrading to vSphere 5.5 and HIT to VSM 4, my new vCenter could not connect to the VSM server at all. 1. Should VSM ip address be configured on the management or iSCSI network? 2. I have 2 vCenters at HQ and DC respectively. In this case, do I need to install 2 VSM, each at each site? Note that while my management and VM networks at both sites are all connected thru VPN, the iSCSI networks are isolated. 3. Is it possible to deploy both VSM 3.5 and 4 so that both vmware Web Client and VI Client have access to VSM features?
vCenter could not connect to the VSM server