In LM2596 switching regulator datasheet suggested to use low ESR capacitors. since I'm going to use LM2596 as a pre-regulator for a linear regulator to reduce the voltage drop on linear regulator, is it still necessary to use low ESR capacitor?
Use Low ESR caps in the feedback loop and for the filter capacitor after the inductor. The input capacitor, is not as important, but the design might incur more loss and have slightly higher ripple with a higher ESR on the input capacitor. I believe the regulator will help with regulaton, especially with short traces. The best way to find out if the design will be tolerant to a low ESR cap is to simulate it in SPICE.
You will note that the recommendation for a low ESR capacitor is to maintain stability of the control loop. Even if you are regulating after the LM2596, you would still want to maintain proper stability. Use the recommendation of the datasheet and go with the low ESR cap.
It is extremely important to use capacitor that is withing the allowed ESR limits, but as low as possible, because linear regulators can be bad at handling high frequency ripple so less ripple is better. If you look at LM338 datasheet, ripple rejection is very near 0dB at 150kHz and it can even amplify ripple at higher frequencies. Consider adding extra filtering between regulators, or consider if some other regulator is better.