When I bought a Sporty in late 1999 the dealership had local T shirts, and never stopped carrying them. Maybe the MoCo required their blessing on the designs?
Every HD shop now offers store-advertising shirts.
People collect ‘em to show where they’ve been.
If by blessing you mean pay through the nose for a co-branding license, then yes I imagine they could. Bartels in LA has their logos on the back of official HD merch. No idea if they bought a license or are so big they do whatever they want. Our local HD dealer sells a full line of HD merch, none of it has their name on it.