Yes, all mass-produced/manufactured range hoods will have a seam of some form or another. The only exception are custom-made hoods, where each seam is welded and polished over, which adds significantly to the cost and production time.

In order to make a range hood height-adjustable, the chimney must telescope, so there will be 2 sections, which will result in a horizontal seam.

However, keep in mind that high-quality range hoods will have perfectly straight and minimal seams, due to the precision machinery and strict quality control in the production process. Cheaper hoods may exhibit irregular seams, discoloration along the seam edges, and/or very visible mismatches between hood elements.