I would ask the Exchange guy what tipped him off to the fact that the OAB wasn't generating properly? I would suspect he likely found an error in the Windows Event Log. I would then create a Windows Event Log Monitor to watch for that event and alert me when it occurs again. Conversely you can monitor the Windows Event Log the same way using the Windows Event Log Monitor to ensure that the OAB is properly generated every few hours as referenced in the following blog posting.
Managing OAB in Exchange Server 2013 - Exchange Team Blog - Site Home - TechNet Blogs