1. Get the Invisible targets AddOn and make the AI target one of those targets...
3. You can't... (afaik)
4.Why??
I had an discussion of this sort here a while back...
This is actually very hard as the nearestObject is not the most intelligent function, not to mention that the OFP bullets live only 2-3 seconds...
The nearestObject probably wouldn't detect the bullet, due to couple of facts like the bullets speed, which is so high that the environment in which an sqs loop trying to detect the bullet should be absolutely lag free...
Other way of doing this would be adding a fired eventhandler to ALL units on the map which would each execute a scripts that would 'follow' the bullet through it's life-time constantly checking wether it's distance to the given unit is 10 or less meters... Of course, if the given unit could be any unit on the map this would be impossible to do...
Not to mention the cataclysmic strain on CPU when lot's of units would be firing :-X
bored_onions example works on missiles because the missiles tend to travel 'a bit' slower than bullets
For example 'capturing' a bullet from a script executed by fired EventHandler is almost impossible...
If the game lags a bit the bullet 'escapes' the nearestObject...