I finally got an answer and figured I'd post it so that it's out there if/when someone else has the same question (e.g. buys a used hitch from a forum member and wants to install it on his/her vehicle).

I spoke to ECS, who sells the hitch. ECS says the bolts are reusable. They also say that BMW does not sell the hitch hardware separately, leading one to believe the bolts are not one-time-use items. I, too, had seen in the EKG that the hitch components (apart from the electrical module) are not sold separately and accordingly made the same presumption. Simple enough.

Yet I was still skeptical.

I then spoke to my body shop. My body shop has installed, removed, and reinstalled multiple hitches over the years and they have never seen any hitch-related hardware that is torque-to-yield. Further, and most relevant to my question, they've never seen any reused hitch hardware fail. This is more along the lines of the type of answer I was looking for (short of a direct confirmation from the people at Westfalia who, by the way, are impossible to reach).

So there you have it. YOU CAN REUSE THE HARDWARE. I'll be removing and reinstalling the hitch and reusing the same hardware.

Hope this helps someone else out in the future.