You didn't mention which Moodle version you are using
The steps described below are for Moodle 2.0.4+.
When you create the role, you must first set the option, Context types where this role may be assigned, to: System and Category.
Next, set to Allow the listed capabilities under each of the following sections:
View participants (moodle/site:viewparticipants) - allow the enroled participants to be listed in the grader report.
Set to Allow the "Use ___ grade export" capability of the export formats you want to use; for example, if you want to export grades in Plain text or Excel:
Grade export: Plain text file
Use text grade export (gradeexport/txt:view)
Grade export: Excel spreadsheet
Use Excel grade export (gradeexport/xls:view)
Grade report: Grader report
View the grader report (gradereport/grader:view) - allow the user to view the grader report.
View courses without participation (moodle/course:view) - allow the user to enter the course without being enroled.
Export grades (moodle/grade:export) - allow the grades to be exported.
View grades of other users (moodle/grade:viewall) - allow the Grade icon to be displayed in the Course administration section of the Settings block.
Once defined, this role may be assigned to a user at a System or a Category context.