Got off the phone with a representative and was told it is possible.
Could anyone guide or assist me in wiring up a keyence 3-wire NPN sensor?
Keyence Sensor in question:
I don’t see how it would be possible. The sensor needs 24V and 0V to power it, and its digital output produces 0V (NPN) instead of 24V (PNP).
The UR control box will need 24V on its digital inputs. It’s only possible to set NPN on the tool I/O. 
Can’t they just add a relay to the circuit?
Sensor pulls the relay’s coil to ground, and a +24V source is switched through the relay output to the control’s digital input.
Could that be a solution? I’m away from the robot right now but will test it tomorrow.
How are you using this?
I’m not really experienced with these – I was assuming this was a basic on/off sensor.
Looking at the schematic, it appears that the orange wire will give you a 1-5V output indicating the signal strength.
This could be tied to an analog input in the control and you can program in whatever logic makes sense for signal values.
If the black wire is just an on/off signal, then what I described with a relay should work - with the relay’s coil as the load, and the relay output going to a digital input.
Hopefully someone else will chime in to say whether I’m making sense or not.
Keyence sells a PNP output converter we have used before. If you didn’t want to purchase this, you could replicate the circuity with (I believe) a relay and pull-up resistor. The documentation for the product at the link should answer your root question.