I was able to solve the issue. Rebar doesn't give any geometry. So all trial to generate dim from Rebar was failing.
The method I tried was with the ActiveView, selected rebar Options.
Snippet
Options options = new Options();
options.ComputeReferences = true;
options.IncludeNonVisibleObjects = true;
//options.DetailLevel = ViewDetailLevel.Fine;
options.View = uiDoc.Document.ActiveView;
If I select the Geometry Elements from this and filter only lines, I can get the reference of that lines.
Hope this helps someone in future.
