definately injure yourself doing those exercise thingy's, u should double pump your delts with 10lb dumbells,lol.
I think your form looks pretty good and u look like you could lift alot more, can u power clean what u can push press? Must have been alot of bodybuilders in the rehab section and never seen a push press. Your lower back doesnt round so i cant see anything wrong with it. I also have lower back problems but find weight training/oly lifting actually helps, especially overhead squats. A second look at the video, u maybe pressing abit out in front instead of directly overhead(the first few reps anyway) but Im being very nit picky, otherwise its good.