I'm no groundhog expert, but I didn't see any bending in the lower back. It looked like the bending was in the mid-back- AFAIK that's a bit of a waste of power and makes the lift a little harder but it's not harmful.
To me, it seems like you're rushing your setup. You squat down, then your hips raise, then you start pulling almost immediately. A bit like a lot of Oly lifters pull- but I think for DL it is better to spend a bit of time getting set in your pulling position and making sure you are tight as hell. Are you "pulling the slack out of the bar"? For me the point of this is also to "pull the slack out of your body"- by pulling a little bit you can feel where you are loose and tighten everything up.
I'd hold on for some more/better advice though- there are some strong and experienced lifters here, one of them will show up at some point.