SMSMSE 7.x is certified to be installed on SCR environment.
SCR is disaster recovery (DR) solution for Exchange 2007. It uses the concept of sources and targets as active and passive copies of storage group.
Some useful links about SCR:
Below is reference from Microsoft Technet:
The source can be any of the following:
• Stand-alone Mailbox server
• Clustered mailbox server in a single copy cluster (SCC)
• Clustered mailbox server in a Cluster Continuous Replication (CCR) environment
The target can be any of the following:
• Stand-alone Mailbox server that does not have Local Continuous Replication (LCR) enabled for any storage groups
• A standby cluster, which is a failover cluster where the Passive Clustered Mailbox role is installed, but no clustered mailbox server (e.g., no Active Clustered Mailbox role) has been installed in the cluster