The amperage of the power supply won’t affect the Photon, so that’s not a problem. And 5V is fine on VIN for the Photon.
The only concern is voltage spikes caused by the WS2811 turning on or off rapidly. This is dependent on the number of LEDs and the quality of the power supply. It’s probably fine, but can’t be guaranteed. Large capacitors may help, or the power supply may already have them.