I'm pretty sure it does not count bullet hits, but damage. Perfect example is the Spit 1 vs. Typhoon analogy posted earlier.
If you take a 110 and give a good spray to each GV you see, you've given out a lot of damage, though you might not have hurt it.
A 110 spraying will beat out a p51 spraying anyday.
2-30mm's and 4-20's can deal a lot of damage. But in the case of t34, Panzer and Tiger, it'll only just scratch the paint job.
It's real gaimy, but there are people out there who will take a 110 and spray everyone to get the kill.