Simply, if you charge directly into an enemy, they won't take any damage and be pinned for the rest of the charge; if you only just graze them, they'll take 50 damage and be knocked back, just like what would happen if you charged into them after pinning another enemy. All of this seems to completely ignore relative height, i.e. there's no vertical graze boundary, and you'll always pin an enemy even if you're just touching their foor or their head, but this scenario is harder to find in regular gameplay.
Imagine, if you will, a spherical Reinhardt, and visualize how enemies' bodies would react to a 200+kg metal ball flying at them. If the enemy were to only touch one side of the sphere, they'd take damage from the hit, of course, but they'd be pushed aside instead of dragged forward. Now if the Reinball were to hit an enemy directly head on, so their body was directly in the way of the center of mass of the sphere, they'd be moved in the same direction as Reinhardt is, dragging them along for the charge. I know it's somewhat of an abstraction, but it works very well to get an idea of how pinning works. I've made a diagram to explain what I mean:
Of course, this is all based on my experience, but it seems like an accurate model.
Reapers ultimate actually hits everything around him in an 8 meter radius (360 degrees).
Quoting from my link:
Death Blossom is a very deadly short range damage dealer that does 360 degrees of damage all around Reaper. Deathblossom is best used when there are a lot of clumped up enemies in a short radius, as it can wipe all of them out easily as long as they do not kill you first while executing Deathblossom.
For more info you can check this: Reaper strategy guide
People have also been talking in reddit
Quote from Reddit link:
Currently, Death Blossom's hitbox extends way above what it appears to hit. A reaper is able to ult on the ground and kill a pharah well above him. The hitbox needs to be changed to fit the animation or the animation needs to be adjusted to fit the hitboxes because it's extremely frustrating to play against.
It seems Reaper fires in all directions. His animation demonstrates that.
From this Ability Preview Video you can easily see flashes of red diagonally up and down. Demonstrating that he does fire up and down.
Best Answer
It's quite not a very good researched Answer but one, that come up if you play him one round:
Yes he get Soul Orbs but not for every Omnic. I can't really say if he get only one for the "special" Omnics or normal too but he get some.