The fact that you're connecting a HiLook IP camera to a Pro-Series analogue DVR is likely why the option is not available on your recorder but is for the analogue cameras.
The HiLook range uses different software to your DVR, which will be the main issue.
With the hybrid DVRs, you're often also limited in what you can do on the IP cameras that are on them.
Is the firmware on both the camera and DVR up-to-date? If so, it will be due to limited compatibility between the PTZ and DVR, which is why the only way of using face detection would be to do so on the camera only, with it recording local storage (microSD), rather than the DVR. You would need to use a HiLook DVR with the PTZ to have full compatibility between the two.