They probably stole the video off of denis. YouTube ads for scam sites often rip clips from famous people. I remember some shitty mobile game using a video of Pyrocynical in their ad, without his consent.
There are also several Twitch-channels streaming VODs of s1mple streaming, but they have covered up his usual stream overlay with scam links that say you'll get a free knife.
Besides the clip with denis in it is probably not owned by denis, so even if they are using the clip with permission, they didn't get permission from denis.