Likely he is fine (besides being an unsafe idiot for drinking and driving).
If by “He received a DUI” you mean he was pulled over on that day and charged then he hasn’t yet been convicted, even by the definition in 46 crf. And at the time he applied he did not have a conviction.
If he holds a current valid credential then he has no obligation report a conviction until his next application of any type.
There is a lot of good information and applicable links and definitions here: