Although both your examples are grammatically correct, it is more likely in context that you would simply refer to employees.
However, you might include the article the if you had previously referred to either employees or the employees, as in:
All employees will be expected to familiarise themselves with the code-based approach to office ethics. This approach enables the employees to know up front what is morally required and expected of them at work.
Here the article the serves to reflect your previous reference to the employees concerned.
However, it works just as well if you omit the article. It's really a matter of preference.