If you want to use this type of datagrid, you need to specify a helper object that can keep track of the object count. Create a dataview that includes that count in an attribute. Put the datagrid within that dataview and use visible conditions to show the datagrid based on the expression:
$dataviewHelperObject/CountObjects > 0
Consider upgrading to Datagrid 2. It has empty state functionality out-of-the-box. You can find it in the data widgets module.
If you are looking to prettify you page, consider using the badge of the tab to show the number of objects.
Where test is the attribute Ruud suggested to create