Just talked with Warn, and the snap ring (retaining ring) and splined washer need to stay on the axle shaft.
Their instructions do not have "(retain)" printed next to the retaining ring in the Automatic Hub removal image in Step I, and it should.
Step III shows the retaining ring going back on, but the image is of a Toyota hub.
The snap ring and washer stop the axle shaft from pulling out of the hub as the suspension cycles.