Sadly I have suffered same issue and, after a whole week of researching, we have had to accept that RecoverPoint SRA is unable to automatically add hosts to a storage group.
Reason?? It looks pretty clear once you realize that SanpMirror only manages replica, it doesn't perform any operation at storage mapping level, so in order to be able to perform a failover (real or test) you have to create initiator for ESXi hosts (if you haven't already created) and add replica volumes to a storage view which includes those initiators.
This is what we made in our environment (RP 3.5 + VPLEX) and it worked, but as VMware said, I think EMC's SRA should be able to perform that operation (other storage solutions we have on our production environments, such NetApp or NSeries, include that functionality)
Nevertheless, we are in contact with bot VMware and EMC to try to find a workaround that allow us to automatize mapping process.
I hope this helps.
Kind Regards,
Sergio Oliva