It does work, but that's not going to help you with the hummers.
Most likely, the reason your flash isn't firing in FP mode is that the Commander setting for the built-in flash is not set to"--". You have to disable the built-in flash when using AutoFP. Set the built-in flash to "--", select a shutter speed faster than 1/200s, and you should get AutoFP operation.
But this won't help with your hummers. In AutoFP mode, the flash acts as a continuous light source. This is necessary because your camera has a focal-plane shutter. So lets talk about FP shutters.
FP shutters do not have shutter speeds of 1/4000s or 1/8000s. Those are *effective* shutter speeds. That is to say, you get the exposure effect of 1/4000s. The actual time spent performing the exposure is much longer...somewhere in the 1/300s range. That's how long it takes the curtains of an FP shutter to travel from top to bottom.
I'll tell ya right now...a hummer's wing travels a long way in 1/300th of a second.
People who are serious about hummers will set up two or more flash units close to the feeder and set to their lowest power. At its lowest power, your SB-800 has a flash duration of only 1/41,600s. THAT will freeze a hummer's wing. You can place the flash unit about one foot away from the feeder, and shoot at f/11, 1/200s, and ISO 100. With the feeder in the shade, those settings will underexpose the scene by 3 EV on sunny days...just what you need to have your flash provide all the light. And if 1/128 output end up being too dark, try 1/64 power...that's still 1/32,300s.
On page 98 of the D80 English manual, Nikon says, "Auto FP High-Speed Sync is not available when using the built-in flash." However, Nikon leaves it to you to "connect the dots," so to speak, on using Auto FP in wireless mode.