First and foremost, the current release of SRM at the time of writing is 5.1.1. SRM must work with same version of vCenter. So if your vCenter is 5.0, you can only run SRM 5.0. In order to run SRM 5.1, you need to upgrade only your vCenter to 5.1 while vSphere can remain any version that is supported by vCenter 5.1. In this case, vSphere 4.x and above. You can check out the interoperability using the site here. Here is an example:
Next, we know that SRM 5.1 support vSphere Essential Plus. That is true however if you are using a lower version of SRM, vSphere Essential Plus is not supported. ONLY SRM 5.1 supports vSphere Essential Plus. Read the SRM FAQ guide on page 3 and page 5.
To find out the vSphere edition supported, you can refer to this site. Below is an example:
With the vSphere supported, there is the question that goes to vCenter edition. As we know there are 3 favours of vCenter, Essential (from Essential or Essential Plus kit), Foundation (limited to 3 hosts) and Standard (no limitation). SRM 5.1 will support all 3 editions of vCenter but any version of SRM prior to 5.1, will only support vCenter Foundation and Standard Edition ONLY. This is due to the support form SRM 5.1 on vSphere Essential Plus for that vCenter Essential is supported.
If you are run Essential Plus at both Protected and Recovery site, this is supported on SRM 5.1 with vCenter 5.1.