Steps to reproduce:
1. Create a course site with at least 2 sections.
2. Add roster tool.
3. Login as an student of one section.
4. You won't be able to see roster.
If you grant roster.viewgroup permission to student role then you see the list. I think this permission should be granted by default in Sakai OOTB.
It has no sense grant roster.viewallmembers to student or even instructor.