Is it legally required to report DUI or no?

Well if they find out that you lied to them and did not report the conviction then they will fire you.

It sounds like, when you filled out the application, you hadn't been convicted, yet. If you've only been arrested, you're not lying by checking "No" to a question that asks if you've ever been convicted. If, however, you are subsequently convicted before they do a background check, you might have some explaining to do. If you have been convicted, it will show in your public court record which they can easily find.

The company has a right to ask for criminal convictions as part of an employment process. Since they are giving you a car allowance, it is evident that they expect you to drive as part of your job. Such being the case, knowing you have a DUI conviction may well be a critical piece of information. Your insurance company is misinforming you. Criminal records are public records. All I would have to do is have your name and date of birth and I could find out what kind of cases (civil and criminal) you were a party to. I may not be able to know the specifics, but I would know that you had a DUI. You can go ahead and try not to divulge this information hoping they never find out, but if and when they find out (and they will), you will be immediately terminated for providing false information... yes, omitting information is providing false information. If you were to be driving for business purposes and be under the influence and get in an accident, and cause injuries, no doubt the company would be sued. Sadly, the consequences of a past poor decision.