From experience, I can tell you there likely is not a good business key for employees.
It depends on your goal. You may be able to use Company + HRID in some cases. In others, the HRID changes ever time the employee changes department, or is rehired. This makes it hard to 100% of the time link them.
You are better off using a surrogate key and mapping the business key to the surrogate key. This will allow you to manually link them in the future, if you find the HRID changed for rehires, etc.
All other options you listed are not good. All those can and will change over time. If someone types the DOB wrong, and corrects it, it becomes a new employee.