Under Commitment your directors are asking how deeply you are dedicated to the band's purposes and values. How important is the band in your life? Are you willing to make personal sacrifices to achieve the band's objectives? —to dedicate the necessary time to practice, to meet all rehearsals promptly, to maintain your instrument and uniform, to put the band’s needs above your social and recreational pursuits?
Under Work Ethic your directors want to know how diligent you are: are you satisfied with doing what's minimally required or do you try to make the most of every task and assignment? Will you put in the effort needed to memorize music and drills, master scales or stickings? Do you regard your work as a chore or as an opportunity to grow as a musician?
NOT DIRECTLY ON TOPIC, but because the question has been raised:
The contemporary sense of work ethic described here is much reduced from the sense in which the term was invented by Max Weber. Today it means little more than diligence and reliability; in Weber's formulation it was a specifically Protestant theological understanding of work: that hard work and frugal living were not means by which one earned salvation but signs that one was predestinately chosen by God to be saved.