Thanks for your answers! Against the guidelines our APs which were connected to our ZD seems to connect to the cloud without a reflash wihth the single AP firmware.
I disabled the DHCP vendor option for ZD discoveryin our AP management network, set the AP manually to default settings and it connected to our cloud demo controller. The only problem which seems to stay is to set the AP to default settings, maybe i can do this via SSH in order to not be physically at each of our 350 APs.