Ive been rammed when i was in no way attempting a HO.
One time i lost my tail when a yak flew into me. The point is one gets away scott free in a situation where both would be wrecked.
If someone gets a kill because the other guy has collided with him then there should be some kind of damage or penalty for getting the kill that way.If like you said only one guy sees the collision all the time then the theory of 2 people both trying to HO each other is a myth!

When i do actually take a ho shot i usually fire at a distance and evade.This doesnt however always work and quite a few times ive been surprised by the collision.The people i see ramming me are usually firing all the way past without so much as a touch on their ailerons yet they fly past and i lose wings. If like you said they dont see the collision or arent pointing their nose right at you then why would they still be firing?.If they are BOTH trying for the HO they should BOTH pay the price. If one sees the HO and the server sees that the other DIDNT then no damage should be applied or moderate damage to the guy who DID see a collision(maybe loss of a whole wing full of guns would work here).Surely it would be possible to check what both FE's are seeing.
People are actually abusing the present system too by simply flying close to another aircraft and weaving around when they run out of ammo.On their FE they just wizz past very close but on the other guys FE he sees a collision because he sees the aircraft in a different point in the sky.If you dont think this would work take a look at a large number of players launching off the CV. On their FE they are on the deck but on others they can be as much as 300-400 yards away floating above the sea but still taking off.Apply this to an aircombat where you NEED to get within 300 yards and you get the overlap of positions which causes collisions. Happens in the scissors as mandoble says.