Here is some info on the back side of the quart of Schaffer oil.
That in no way reads as Harley endorsing the product. Though it's obvious that's the intent they're hoping to portray all that says is the oil happens to meet to same ASTM oil specifications that Harley as a manufacturer requires for its products.
This would be no different than if the old Internic had a "standard" for posting online that all users should use Calculators to double check any math they might do as a user, must do so Universally every time they did so, that they also had to learn site Navigation to be certified as a site member and also had to type in ansi Text. So to be safe and efficient net user you had to be proficient with calculators, use them universally, be familiar with site navigation and ANSI text.
Assume then that Neal had a specification for membership here that all members should use this standard. The text on that bottle label would be no different than my then putting as the signature line at the end of every one of my posts that "This bottle of posts meets the Neal approved C-U-N-T specification as defined by Internic for posting." Neal (the Harley analogue in this example) isn't saying I (the oil manufacturer in this analogue) am C-U-N-T certified, capable, nor in any other way C-U-N-T (or Harley/Neal) endorsed. It's only me, with no third party acceptance, saying that I happen to be adhering to the same set of standards that Neal, also, happens to say is correct for his product.
So while Shaeffer might indeed have to pay HD for what's done there they're not paying for an endorsement by HD (since there is no endorsement there). The more likely option is they're paying for the privilege of putting the HD logo on the bottle just like every other t-shirt vendor, coozy seller and other third party hawker gets sued by Harley to do if they use the Harley logo on a commercial product.