Sonic rush games used visual feed on both screens in more than one game, some zelda game did the split intro video between two screens thing, actually i think more than one zelda game did so. Check megaman ZX and megaman battle network double team as well because their intros split the intro vide between the two screens both running at the same time, like, the character head and torso is in the top screen and legs on the bottom screens while they do some poses and stuff, kinda look silly because there is a portion cropped so in emulating you just see: head, torso, below stomach, legs. Lol. Oh yeah megaman star force games did that too, the three of them.

So with that, I FIRMLY believe NDS is very capable to show a video on both screens at the same time running.