He HAS been "formally" charged if he has been charged. If they didn't find it in the background check and he didn't already disclose it, why would he now? At least he can keep the job for a while.....
He needs an excellent lawyer on the DWI. Houston is NOT a friendly venue.
Are you asking for the legal answer or the moral answer? Yes there are different here. Legally you don't have to disclose anything that is against your own interest. However, if you want to be trusted and viewed as one with integrity Telly your employer what is happening and that you are working on it. Get an experienced criminal defense attorney in your area to fight this battle for you.
I am not sure what you mean by he has not been "formally charged" but if he has a charge pending, I agree with Ms. Henley, he has been charged. I think the answer should revolve around how the company application posed the question. If they asked if he had been convicted of a crime then obviously he has the right to say no. If he lied on the application as far as whether he has pending charges, then most employers would look at that more disfavorably than if he simply has been charged with a DWI for which he has not been convicted. If he answered the application questions honestly, then I again agree that he should wait until the background checks come in at which point he could explain the situation and that he has not been convicted. Good luck!