HR Data - Slowly Changing Dimensions

I am working on an HR report and have a type 2/slowly changing table called employee_data (the table has a "from date" and "to date").  data changes per employee infrequently, but when data changes the employee gets a new row where from date = the date the transaction is entered, and to date = a date in the very distant future. The employees previous row is updated with the 'to date' being the day prior to the new row. I also have a date table with one row per day. 

I'd like to create a report that shows the count of employees per month, but dont seem to be able to find a way to create a join from the date dimension to the employee dimension using "between".

Any suggestions on how to best achieve a join from a slowly changing dimension to a date dimension such that if the month grain is chosen in a report, that the employee is counted every month for which they have a valid record (based on the from and to dates)?