Is an employee required to apply for FLMA. We have an employee who wants to use their sick/vacation and not apply for FLMA.

If you know the absence would be FMLA-covered, it would be a violation of the Act NOT for you to designate it as such. This does not preclude your from requiring the employee to used paid leave in conjunction with FMLA leave, or to request paid time off if your policy does not require it.