Unfortunately, it is heresay. The cops can't do anything unless they catch him in the act. I could just as easily say I observed you driving recklessly as well.
Back when we were in high school, a bunch of us in RX7s, Civics, Integras, WRXs, got together on Carmenita Rd. and raced up and down at night time. The residents called the cops on us and converged on us. yeah we were stupid. We were all parked in the parking lot and cars would race up and down the stop lights. When the cops arrived, the race wasn't "happening at the exact moment". The cops blocked us off and asked us who was racing.
Long story short, everyone of us got fix-it tickets and what not. Nobody went to jail nor did we get speeding tickets or exhibition of speed tickets, etc. Why? Because cops know, they got nothing on us, unless they SAW us do it. Same thing, the residents can file a complaint, but you can't prove it, so you best have video. The only thing cops can do is run your record, try to stick you with whatever stupid shit they can get away with like:
1) no front plates
2) object obstructing mirror
3) tint on front windows (you're not legally allowed to have front tint on front windows that is below 35% light transmission).
4) Non-carb approved intakes, etc.
We would get fix-it tickets for shit like that.