Overview:
It is possible to add Personal / Shared workspaces to the portal navigation hierarchy.Workspace cannot be added as an entry-point, only as a second level entry (or lower) in the top-level navigation of the portal.
Version : EP 7.3 , Enterprise Workspaces 1.1
Prerequisites :
Personal or Shared workspaces should be created as per wiki : http://wiki.sdn.sap.com/wiki/display/EP/Use+Enterprise+workspaces+in+EP7.3 .
Technical Details :
1. Collect Workspace ID which need to be displayed under any portal role :
Login to Portal and Navigate to Workspaces -> Workspace Directory and check the created workspaces.
For personal workspaces , Workspace ID is personal
For shared workspaces , open the created Shared workspace from workspace Directory and choose Workspace settings icon as shown below.
Choose General Properties tab and collect the Workspace ID value from ID field.

2. Add workspace to Navigation Hierarchy :
Open the role / create the role and set entrypoint which should be displayed on top level navigation. Open the properties from property editor of role and select the property External Connector. 
You can set External Connector value in the format workspaces://<key>:sortPriority=<number>, Here Key is workspace id and Sort priority decide the position of speciifc workspace in navigation. Observe from navigation hierarchy as shown below.
