Is a protection diode needed for a resistive load?
If the load is a resistor you should be safe without a diode. Resistors have a parasitic inductance of some sort but the inductance value is usualy very, very small unless you are dealing with high power wire wound resistors that usually have a (somewhat) high parasitic inductance.

Have a look here too.

So the answer is no, you won't need it in almost all practical cases.