If the record was totally expunged, then perhaps not. However, if the DUI was long ago it may be best to disclose it and avoid a problem if it surfaces later. President Bush had 2 DUIIs so a security clearance is not automatically removed because of an old conviction. If it was a juvenile conviction, some states allow law enforcement to research juvenile offenses. Recommend disclousre to avoid a problem later if it surfaces.
DOD security clearances require you to disclose all prior arrests (not just convictions) and records of alcohol treatment. Most states do not allow DUIs to be expunged; to prevent a recidivists from obtaining first time offender sentencing.
If you fail to disclose the arrest and the DUI is later revealed by other means (interviewing your aquintances) you could lose your clearance, discipline or termination. Some people have the mistaken idea that once a case has been legally expunged, its ok to deny it ever happened. Honesty is the best policy. Make sure you know what happened in court on your DUI and what records were actually expunged before completing your clearance application and interview. Good luck.
The one thing the government does a good job with is background checks for security clearances. In most states, convictions are not "expunged" as in totally eliminated, eradicated, or forgotten. In Michigan, a conviction may be set aside and the file sealed. This is sometimes referred to as "expunged". The record still exists, but the file is sealed and can only be opened for good cause. While sealed, it is not available to the public.
If you are being considered for a "real" security clearance; i.e., secret or top secret, your conviction will be discovered. Therefore, as a wise man once said, 'honesty is the best policy'. I would certainly check with your attorney in your jurisdiction and seek his/her opinion.
Finally, you do not want to run afoul with 18 USC 1001. What's that? The federal criminal statute that makes it a felony (10 yr) to make a false statement to a federal official.
While the record may be expunged, I suspect the security clearance application asks very broad questions. If you attempt to conceal your past, you will be lying on a federal inquiry. This concealment alone may, in fact, get you charged with a federal crime. It is clearly better to be completely honest and then explain your answer. Regardless, you don't want potential discovery to "haunt" you for the rest of your career.