iPad initial setup join Wi-Fi by scanning QR code
It is not possible to access the built-in Camera app before the initial setup is complete.

As the iPads in question will be configured via DEP, the appropriate approach would be to provision for your device to join the desired Wi-Fi access point(s) automatically via your MDM solution. When done, the iPad will automatically connect to the said Wi-Fi network if it is available, even during the initial setup.