Definitely true. You'll need the ribbing to make the hat fit correctly. A garter stitch hat will not be as stretchy as a ribbed hat.
This is your perfect opportunity to learn the rib stitch on a simple project. GO FOR IT!
When you switch from knit to purl, be sure to bring the yarn to the front between the stitches.
When you switch from purl to knit, remember to take the yarn to the back between the stitches.
When you knit the other side, be sure to knit and purl correctly and in order. If you ended the front side with a purl stitch, you'll need to knit the first stitch on the other side.