Do all devices in a network have to be Wi-Fi CERTIFIED for Wi-Fi Protected Setup to work together?
No. Access points/wireless routers which are Wi-Fi CERTIFIED for Wi-Fi Protected Setup will provide a way for the user to "look" at the network settings and manually join older devices to the network.
With PIN configuration, users can ask the Wi-Fi Protected Setup device for special numbers, called WPA keys, and assign them to legacy devices to join the network. In push button configuration, some companies may offer a firmware upgrade for legacy devices but this will be at the discretion of the individual manufacturer.
All Wi-Fi devices in a Wi-Fi Protected Setup network must be Wi-Fi CERTIFIED for WPA2 security, however. Wi-Fi Alliance recommends that users choose devices with WPA2 security for the most advanced protections.