I can't speak for R18 of course, but VR titles on their Japanese site DMM are only accessible through the various apps for mobile devices, PS4, etc.. So it works differently to regular videos.
Assuming R18 adopts a similar system, the matter of whether DRM is used or not is a bit of a moot point, because you would still have to view the videos through the apps anyway.
The only case where it would matter, is if, for example, R18 provided the ability to download VR videos direct from the website. That would be nice, of course, but I'm not sure how likely that is.
Figured it never hurts to ask, I'm a hoarder at heart XD. I just like to have the ability to watch them anywhere regardless of internet connection. While I'm not a stranger to DRM locked content as I use Steam and Amazon video/music/ebook content, they still allow you to download and then access while not online.