I'm a little fuzzy on your circuit, Drew, but I think the answer is yes.
If the analog input on the PLC is voltage and you are running the loop current through a resistor to create a voltage drop, you can pull the PLC I/O module and the transmitter 4-20 mA will operate undisturbed.
If the analog input to the PLC is current, you can't put a resistor in the loop. The 500 Ohm external resistor would be in parallel with the 250 Ohm internal resistor on the analog input card. The net result is that 1/3 of your loop current would go through the external resistor and give erroneous readings.
Now, a trick I have used in the past is put a Zener diode, reverse biased, across the input wiring at the field terminal strip. You have to watch your voltage drops, of course, but if you use, let's say, a 12 volt Zener and a 250 Ohm impedence input, the zener won't conduct when the analog card (or any other loop device for that matter) is there. If you yank the card the Zener will conduct and the transmitter won't know the difference.