Because of its nature the bi-directional ObjectServer gateway should not be configured to connect to a virtual ObjectServer reference.
The virtual ObjectServer comprises a Primary and Backup ObjectServer. The bi-directional gateway is responsible for synchronising data between the databases of those two ObjectServers. If the reader and writer components of the bi-directional gateway were configured to connect to the virtual ObjectServer reference then the reader and writer would both connect to the same ObjectServer, and not to Primary and Backup as required.
Other ObjectServer gateways can, where appropriate, connect to a virtual ObjectServer reference. For example, the uni-directional ObjectServer gateway in three tier architectures will have the writer connecting to the virtual ObjectServer reference for the collection layer gateway, and the writer connecting to the virtual ObjectServer reference for the display layer gateway.