If you get charged with a DUI and it is dismissed it means that the charges against you were not able to be proven. There are two types of dismissal with prejudice and without prejudice. If your case is dismissed with prejudice it means that the charges cannot be refiled against you and the case is over. If the case is dismisses without prejudice it means that the prosecutor can refile them at a later date.
What happens if your DUI case is dismissed? As a general rule, the fact that you were arrested stays on your record. The fact that you were charged stays on your record. The fact of the dismissal stays on your record. If you received an administrative suspension from the BMV, that may stay on your record unless you are in a state that removes those suspensions if there is a dismissal or acquittal.
You should contact a lawyer in your state to answer this question. There may also be a legal procedure to remove those things or to seal the record.
I don't practice law in OK, so i am not giving you legal advice, just my thoughts based on what happens in my state. Here, a DUI arrest will always show up on a person's criminal history. In most cases, the FBI is notified of the arrest and will remain on their database as well. Scrubbing this arrest record is difficult if not virtually impossible. Thus, if for a job application or other inquiry, you are asked if you have ever been arrested, you would have to answer honestly or possibly be shown to have lied on that application. However, if the question is whether you have been convicted, the answer would be no, given the information you have stated in your question--that is, a dismissal means you were not convicted of the crime. A dismissal stays on our records here in WA, and if transmitted to the FBI, there too. And like the record of a DUI arrest, the dismissal should stay on your record as well. You may be able to obtain a copy of your criminal history from the OK state patrol to see exactly what it says.
Your arrest stays on your record. However, most states have procedures that allow you to clear up your record if the case was dismissed. I would call the clerk of the court in the county your charge was dismissed and ask if the case can be expunged.If need be I would call the lawyer that handled your case and retain him to expunge your DUI arrest.