Is it possible to add chart in Joined report? I tried to do this but the chart is not visible when running the Report.
From Chapter 10 of Force.com Platform Fundamentals:
Joined reports let you create different views of data from multiple report types. In a joined report, data is organized in blocks. Each block acts like a “sub-report,” with its own fields, columns, sorting, and filtering. You can add a chart to a joined report. For example, in the following sample, the joined report pulls data from two report types related to the Positions object. Together, the report shows applications received from job ads posted for each position.
Clearly, the answer is "yes, you can add charts to joined reports". The Analytics Workbook includes a tutorial on creating a joined report. Unfortunately, that tutorial adds the chart to a Dashboard after the joined report has been run, not as part of the report itself.