It depends what format Events Manager is storing the dates in the database in. For the Date filtering to work in Search and Filter, the dates must be stored in the yyyymmdd format (always eight digits, with zeroes to pad, e.g. today is 20180809.
You can (quickly) inspect what data is there using our plugin in the Form UI.
Add a Post Meta to the Form UI. Of the three types tabs, choose ‘Choice’. Select the Meta key for your dates and Under get Options select ‘Manual Entry’. Below that you will now see an option to ‘Browse Values’. A box will appear with all the values stored in the database.