Is it possible to haw one plugin with 2 smart client tabs ( next to live,playback,search.. tabs)

Yes.

You would in the xDefinition have something like:

                    _workSpacePlugins.Add(new XxWorkSpacePlugin());
                    _workSpacePlugins.Add(new XxWorkSpacePlugin2());
..
        public override List<WorkSpacePlugin> WorkSpacePlugins
        {
            get { return _workSpacePlugins; }
        }