Yes. If you want to use a Canvas rubric for the assignment, you must add the rubric before setting the External Tool submission type. Create the assignment with any other submission type, save the assignment, add the rubric, and then edit the assignment to select the External Tool > Turnitin. You can then use the Canvas rubric when grading in SpeedGrader.
This is very important if you wish to have Turnitin submissions but also wish to track learning outcomes/accreditation requirements/competency attainment using the Canvas Outcomes function.