Not at all. Traeger wants you to use their pellets and claim that the controllers are tuned for Traeger pellets. However, people are successfully using a variety of pellets in their grills. I have used Traeger, Expert Grill (Walmart), Pit Boss, Bear Mountain, and Kingsford. Of those Bear Mountain are my favorite. Traeger pellets are rather soft, so they break and create a lot of dust.
Other brands you will find in use are Lumberjack, Camp Chef, Weber Woodfire, CookinPellets, Knotty Wood, and a variety of others. Often people use what is available in their area.
I have not tried the Kirkland blended pellets. I read one comment that speculated that the pellets are made by Pit Boss, but I have no idea if that is true.