Actually, I'm pretty sure that in Destiny there is no real "kill stealing" if I'm not mistaken. At least in regards to PvE. If you are nearby when something dies you will also get xp/glimmer for the kill. If you shoot and hit something, you'll get credit for a kill regardless of who dealt the final blow. At least that is what I have noticed myself so far. Only a few specific bounties do not follow this however, but patrol missions that require you do kill things or get drops of certain enemy types seem to follow these "rules" that I mentioned above.