If you use splash page authentication then the OS fingerprinting works fine, but if you use WPA2 with a PSK or Enterprise modes then the device might not make an http request after login, and consequently per device type group policy doe snot work.
The best option is to use WPA2 Enterprise mode with certificate based authentication. Then strickly only devices you put a certificate on can attach. If you have mostly windows clients this is easier, as you can create a group policy to deploy certificates onto machines automatically.