Again, unless the application says something about only listing misdemeanors that are less than eight years old, you need to report it if you want to be honest about it. Even if the background check you ordered doesn't show it. Not all background checks are the same. Your employer may have ordered a more in-depth background check than you did, or your employer may have ordered a background check from more than one agency. Or whatever.
Bottom line is, if you don't report this misdemeanor and your employer finds out about it (through any means, not just a background check), your employer is legally free to withdraw your job offer/fire you for not reporting it.

