Will lens softness be visible in DSLR video?
You are correct. You're shooting at a much lower resolution on video than stills, and so your effective circles of confusion are much bigger. So you can get away with glass that a decent stills photographer wouldn't touch. This is speaking from experience at work where I share DSLR equipment with a bunch of stills photographers who are always complaining about lenses that I use all the time for video with no problems.

"Get away with" being the critical phrase there. Crap lenses are still crappier than good ones.