A grading column in the Skipper Rubrics is for a crew grade on a task. Thus the Skipper Rubrics serve also as the Crew rubrics. However, assessors are encouraged to skip certain tasks for crew as appropriate. For example, demonstrating leadership skills in not necessary assessment requirement for a crew member.
Also note that a Crew grade is a fallback for when a student is underperforming your expectations as a Skipper of Bareboat Charter Master. You can issue a Crew Grade but follow through with a remediation plan. The weaknesses will be right in front of you as marked in the document or the assessment app.