NeoPixels don't use standard RGB LEDs. They have a built-in control chip whose communication protocol depends heavily on signal timing. If your device isn't specifically built to work with WS281x LED drivers, it probably won't work with them.
The reason is due to the special high-timing-specific nature of the data sent to the pixels. NeoPixels, or WS2812/WS2811, use a single wire protocol that encodes bits as pulses, the time width of the pulses determine whether each bit is a binary 1 or 0. The following is a screenshot from the WS2812 datasheet.
