Who said anything about not trusting your own kid, when there are a dozen other kids and a driver from who knows where on the trip who you shouldn't consider trustworthy. What makes the driver professsional, merely because he/she shows up in a suit and is willing to take the money? You think limo companies don't hire idiots, incompetents and drunks? Feel free to do what you will. I wouldn't trust the driver unless I, (1) knew him/her personally for many years, and (2) see a current DMV report, neither of which is practical or reasonable. I would definitely ask to see the driver's commercial DL, which is required in my state for more than 10 passengers. If you want to trust a driver you don't know from adam, that's your business, however careless and irresponsible that may prove to be. Of course nobody in the back is wearing seatbelts, so a crash with half the kids ejected isn't pretty. Oh, and of course nobody's drinking on Prom night.
I won't get into all the reasons why extra caution is warranted on Prom nights, but let's just say that I've previously been in a position to see the results firsthand when things go wrong, and I might be better qualified than you to judge.