When sharing an Analytics Dashboard who can view and edit it?

If a Dashboard is shared with a Security Group, then users in that Group can view the Dashboard.

The Drill-down to the student level capability of the Dashboard is based on the user's permission to the underlying table(s) for each Dashboard Item

The Dashboard Configuration selected options are automatically read-only when a Dashboard is shared with a Security Group. The Dashboards become "templates" that can be copied, but they cannot be edited. 

A user with Administer permission to the DIO table can see all created Dashboards by any user under "Shared Dashboards" and will have the ability to edit them.