Say your shelf exam counts 25% of your grade, could you get a butt-average clinical evaluation but do pretty well on the shelf exam, and still get a distinction (most likely high pass) for the rotation?...and also vice versa?
Maybe, depending on how much weight each of your clinical evaluations carries and how your clerkship is graded in general.
I do know of a student in the year ahead of me who Honored the clincal part of her surgical rotation and failed the shelf exam, which gave her an automatic Conditional grade for the clerkship. In OB, you have to score 70% to maintain clinical Honors. Several people I know of scored in the high 60's and received a High Pass for the clerkship overall. Therefore, the shelf exams can definitely hurt your grade, depending on how your program works.
On the other hand, in OB, one only had to make a 75% or greater to bump a clinical High Pass up to Honors.