Manufacturer of the iPad Wi-Fi chip I'm monitoring the connected devices in my WLAN. I would like to know if it is possible that an iPad (or another Apple device) has a Wi-Fi network chip with MAC address (OUI) not from Apple, or if it is other device on my network.
All iPads I have ever seen has had their OUI listed as Apple Inc, even though the WiFi network chip is made by others. This has been true for the first generation iPad as well as the latest iPads I have seen.

Of course I cannot know if Apple has made a device with a different OUI - I doubt it though.

Note that it is possible to change a MAC address in software. This means that devices from other vendors can "masquerade" as Apple devices, and vice versa.