I am sure every photographer "worth their lenses" would have "grab" stills from their videos, for one reason or another. They might not have any still shots of the event they were covering and they need to provide a print of that to their client!
For years, publishers has published exclusives news photos grabbed from videos.
In 2010 I grabbed some frames from a short video I did of a rare chance to watch and listen to Ms Zhang Lei, from China; performing on her
Guzheng.