I thought they only pre-screened actual films and not the DIY info type VHS.
They've been known to preview feature films (I know I've heard some of them remark that it's their personal first time watching a film while other members of the panel had seen it before on unfilmed "Bad Movie Nights"), but there's some level of screening for the Wheel episodes as well.
On the one that featured the Therapy Plus scam medical device, as the doctor guy was introducing the product, Mike remarked: "You'll see why they made this video in about 10 seconds." and the video cut to the young lady in a tube top, implying that he watched the video before and knew what was coming.
I can't remember which episode it was, but in another one, Rich remarked: "This is why I put this one on the wheel!", implying that he previewed the video and found it funny enough for inclusion.
To be clear, this isn't a criticism. I feel like the show -- wheel episodes especially -- would be a disaster if they watched truly random videos. The vast majority probably aren't all that entertaining, so I'm fine with the fact that they stack the deck a little bit.
I don't even mind when they blatantly fake the results of where the wheel lands because they're clearly excited to watch whichever video they force. These hack frauds are most entertaining when they're excited about something, and they're not very entertaining when they're bored.