Well, against my better judgement, I actually watched the Kink vid to try and once and for all determine if it is indeed Zack.
The main issue in identifying the man in the video as Zack is that, despite having a distinct face, Zack doesn't really have any obvious distinguishing features (scars, moles, etc) that could easily identify him. Luckily, I did find this from your video:
View attachment 4193376
Whenever Zack raises his eyebrows, a very obvious series of forehead creases appears. These are akin to a fingerprint, and are just as unique. And if you watch the whole video, you'll see that the forehead wrinkles appear with even slight movement of his eyebrows; they're a very prominent feature.
So armed with this, I let my inner
Hank Hill loose, and watched a porno at 0.5 speed while focused laser-like on a man's forehead. It was a chore.
My conclusions/findings:
The man in the video does clearly raise his eyebrows on screen several times, most notably during a fisting section of the video...
View attachment 4193482
...And never develops Zack's obvious forehead creases. At least not that I can see. Maybe if someone else wants to go full 4chan Weaponized Autism and break down each frame of the video in Photoshop to better check, you'll find something I missed.
This could be the smoking gun that proves the Doppleganger Theory, but there are some counter arguments. Namely, the best video I could find is only available in 480p, not exactly high definition, and also it's possible the store lighting is hiding the wrinkles. Though the lighting is quite bright and casts clear shadows under everyone's nose throughout the video, so I don't think this is a lighting issue. But he also might have developed the wrinkles later on, or even had Botox around this time. Many possible explanations.
Ultimately, I can only say that my Forehead Wrinkle Hypothesis is currently inconclusive.
Luckily, I found a moment where you can distinctly hear the man in the video speak. Approximately 24:48 minutes into the film, in the middle of a fisting scene, "Zack" leans forward and mutters "Holy shit." very clearly.
I am terrible at distinguishing voices, but he certainly sounds like Zack to my undiscerning ears.