Yes, I have had "shadowers" too, that is annoying, so I definitely don't do that, But I have taken shots at a ship being engaged by someone else, whether it be to defend my own ship or to try to help, I have done it when a low level ship is taking on a Phantom or a really BIG ship, I know I appreciate a little help when I am up against those big guys as I usually am sailing alone. . and only taking them on for a quest of some sort. . . .
If it looks like they are doing fine on their own, after I see where the big ship's HP is at I will back off and move on.