Is it possible edit/delete/add users, without site administrator role? In some context only(e.g. category, course)?
Adding or editing users is something that affects the entire system, rather than just a particular category, so you probably won't be able to achieve this effectively.
If you're talking about enrolments (i.e. adding or removing people from courses) then yes, that is something you can assign on a course or category basis. But not adding or deleting users from the entire system.