I assume you're referring to OnCommand 5.x Unified Manager. If not, please specify.
In order for OnCommand Unified Manager (OCUM) to discover and report on SnapVault relationships, a few things are necessary:
Both the source and destination storage controllers must be configured & monitored by the OCUM server.
Valid Login credentials and transport protocols must be supplied for each storage controller in the OCUM server.
NDMP login credentials should be specified for each storage controller in the OCUM server. This is required for Protection Manager functionality.
Once all of the above conditions have been met, the OCUM monitors that collect SnapVault information must execute. You can force this to occur with a "dfm host discover <hostname or host-id>" command. Run this on both the primary and secondary controllers in the relationship. Once the monitors finish, check to see if the relationships are listed in OCUM. If you're using Protection Manager, these relationships should be shown in the "External Relationships" menu.