Dependent is the data object type definition - it defines the attributes of a dependent.
Data object type definitions could appear (almost) anywhere but, to be consistent (and follow good OO design) data object type definitions in a Pega 7 application are (typically) created in Org-AppName-Data-DataObjectTypeDefinition.
Dependents is the data object - an instance of the type. We used a rather standard naming convention to indicate the instance of the Dependent data object could contain more than one. Then, because Dependents is an attribute of an Employee, we added the data object (in this case, a page list) to the Employee data object type. Adding the Dependent data object here makes it easy to directly associate a dependent with the employee.
Finally, we define an Employee data object in Org-AppName-Work-...
Does this help clarify?
Let me post a separate response re how to delete the Dependent data object type from SAE-HRServices-Data
1) Click Designer Studio, then select System > Tools > Refactor Rules > Delete a Class
2) Select the class you want to delete. For yor use case, enter SAE in the field, then press the down arrow on your keyboard to bring up the list. I would expect you to select SAE-HRServices-Data-Dependent
3) Click Next, and then on each page after that click Next (accepting all the defaults)
Now, time for a WARNING
There is no undo or restore or cancel or any other way to save you if you make the wrong choice or change your mind. Also, before you delete this class, you need to understand how much of the rest of the application is referencing that class. For sure we know the Employee data object type defnition has a reference to Dependent, so once you delete the Dependent class, the Employee data object type defnition will start to complain.
Based on what you have reported so far, the Dependent data object type definition has the correct applies to class, so why would you want to delete it? It seems what you really want to do is make adjustments to the definition of the Dependent data object type?