Grid Control Standby database status: Creation status unknown
There's a MOSC note, and while it's specific to versions 10.2.0.1 to 10.2.0.5, maybe it worths testing.

The note states that when creating Standby using grid, there were some issues and the remaining part of its creation was done manually.

The recommendation is to remove the Standby DB from the Grid in order to clear the errors, and then rediscover the Standby DB.

For complete reference: Doc ID 1455165.1