All crimes show up on a background check. Honesty is the best policy here. Good luck.
This is not intended as legal advice. No attorney / client relationship exists because of this response.
Your DUI is still a criminal conviction, even though it was a traffic offense and only a misdemeanor, which means it will show up on a background check. However, pay close attention to the way the questions are asked on your background check. If it only asks about "felony" matters, then you wouldn't need to disclose this DUI offense. Most background check forms nowadays ask about ALL criminal convictions though, which means you should disclose it if that's the case here.
It all depends on the ultimate disposition of your DUI. If you successfully completed the ARD program, there is a chance that it has been expunged from your record. Some counties will automatically expunge upon successful completion of the program, some make you file an expungement petition, and others make you wait a number of years before they will begin the expungement process. It all depends on what county prosecuted you.
If you didn't complete ARD, then it will appear and you cannot get it expunged until you reach age 70 or die. I know that sounds ridiculous, but that's the law in PA.
Even if you completed ARD, there is a chance it may appear on a private background check. If those companies caught the charge prior to the expungement they may not have eliminated it from their records. They do not have to abide by expungement orders, but most have a process to contest and correct their records.
The easy way to find out if your DUI will appear is to request a background check from the PA State Police. A quick Google search will get you to the correct page. The bad news is that it will appear on your driving record even if it has been expunged.