Yes, FastLED library can work with Neopixels on Simblee. But the Adafruit Neopixel library doesn't work well with this Simblee. FastLED also works better when you have UI event.
By the way, there is a new Low Power version of Neopixel called SK6805 available on Amazon now. It cuts power by ~70%, using 5mA per LED or total 15mA per RGB LED when compared to WS2812B of 18.5mA per LED or 55.5mA per RGB LED. You don't need to sacrifice color resolution for by lowering brightness to save power.