Hey BJ, hey Tom,
I don’t know if the manufacturer put a screw on Z ball nut (that could have been lost later due to vibration, what I assume that you are wondering); I can’t look because I have difficult access to our machine at the moment, but I just had a look at the manufacturer’s FAQ posting Onefinity Maintenance, and at this moment in the video you have to remove a screw from the Y oil ports before being able to oil it, same for X oil port, but at this moment in the video, you are told that Z oil port is located behind the bearing and would only be accessible by removing the bearing. So instead of accessing oil port, you are told to flood the top of the Z ball screw with oil. Wouldn’t an open screw hole make the oil flow out on the side? Or is flooding meant as FLOODING 
Replacement 1610 Ball Screw Nut.
Replacement 1616 Ball Screw Nut.
So according to the video, at least on Y and X axes, there is a screw on oil port, but interestingly the ball nut here does not look like the offered replacement part:
Did the parts change at some time? The oil port screw here is at 90° while above it seems to be at some 45°?