can single monitor be associated with multiple monitor groups

Yes. A Monitor can be associated with multiple Monitor Groups using the Associate Monitor option. Follow the given steps:

1. Click on the Monitor Group. You will find Associate Monitor in the left frame under the Application Links section.
2. Move the mouse over it and click on the Monitor Type. It will list its respective Monitor.
3. Select Monitor and click Finish.

Similarly, you can add the same Monitor to another Monitor Group by following the above steps.