pulseIn() blocks and these pulses are a few to many ms wide.
Even at over 60MPH a single pulse cycle (start of one to start of the next) is wide enough to get velocity with every pulse without resorting to direct hardware manipulation.
With a red-green led you could indicate the spoiler PWM signal as green, red, amber or off/no power on the same led.
Yes there are RGB leds but the bulbs of those need a diffuser to look like colored dots where the RG leds do not and cost way less.