My neighbors have 6 dogs that will bark, run, and greet anyone that comes down their long driveway on 60+ acres. Last year they were pepper sprayed by a local policeman that got out of his car and walked up to their door (wrong address and he no longer works in the area).
I did not see this, but I did see the same dogs run up and greet a 7 year old little girl who's daddy working at the barn didn't notice she had wandered off to play. The dogs ran to say their hellos and got petted by her as she came up to the house.
Some dogs will go nuts when they see someone in a uniform. When we were kids, the family poodle acted like he wanted to kill my older brother when he came home on leave. Once he changed out of his uniform the dog was back to being a foo foo.