Do cameras pick up sound really good?

Definitely depends on the camera. Most low to mid range microphones are designed to adjust based on current noise levels. This means that if it's really quite, and someone is talking, it will pick up their voice and make it the appropriate level. The problem with this system, though, is that when they stop talking, the microphone will adjust to try to continue to pick up the voice. This makes the background sound get dramatically louder. The opposite is also true, in that it may not distinguish the voice you want it to hear, and will instead lower the sensitivity because of the amount of background noise. Of course, this question needs significantly more information to be answered, but in general, a low end camera or cell phone would not work well in this situation, and even high end cameras are not as good as dedicated microphones.

Depends on the camera. if it's a high quality camera you could somehow hear him if the person is near and it's loud further. but if it's a bad mobile phone or bad quality camera you wound't be able to tell anything it'd be just plain noise.