Once again, everything I say is from what I recall, so I apologize if it seems inaccurate compared to what you have read or seen. For grabbing out of blocking, it takes a bit more timing, it didn't appear like it was a way easy thing to do. You would really have to wait out your opponents' barrage, and get your grab in when you could. In this game though, it doesn't appear as if though getting grabbed a lot is as devastating as it is in SSB, since you can reverse grabs pretty effectively.
That's not to say that you can't do damage with grabs, as they change significantly between all the characters and depending on whether or not you are near a wall (some of which in particular I don't think you can Ukemi from if you miss the grab break).
In the air, there were no "Up + B's". Example, from the ground, Mikey has the rising thunder move from TMNT Tournament Fighters (a dragon punch with a spinning nunchuck". If you perform it in the air, he doesn't get an lift from it, he just performs the move in the air. So you couldn't use it for recovering. I think since no one really has an "Up + B" recovring becomes more a skill of wall jumping and wall climbing, while avoiding an opponent who is trying to prevent such recovery. As you noticed, many people in the 1up video were dying in the Rooftop stage, because those skills came greatly into play there.