Apple seems to say hiding your SSID will not protect you:
“This opt-out doesn't work for hidden networks because they make their network name available only to known devices, so other devices can't detect "_nomap."”
So IIUC, if you hide your SSID and an Apple spy (read: normal iOS user) connects to it, their device will ignore the _nomap token and report your AP to the mothership. And note as well that a hidden SSID only makes your AP invisible in the absence of traffic. iOS devices can probably see and process traffic that happens to be in motion when they are in range.