The McGraphToolServer instance exposes properties that you can examine to determine which McGraphOverlay instance, if any, has an active tool (this is the McGraphToolServer.ActiveOverlay property).
The McGraphToolServer.ToolClassName will be McGraphToolSelect for the built-in select tool and an empty string for built-in graphic object creation tools. It will be the ProgID of an active custom tool.
The McGraphToolServer.ActiveClassName will be the class name of the type of graph object being created (e.g., McGraphObjRect). It will be an empty string if the selection tool is active.