so here are my concerns Scale Horizontally within same Data Center, primary server which has admin running goes down, the second server is of no use in case of DR, is there a way to achieve without using the same hostname in DR?

Thanks any idea on this I am trying to install a second instance over the same DB and getting an error that the STB have already been used

Thanks, but my question was more on Groups ie create a security group in MS LDAP and then use that to control the roles in OAS ?