Android Enterprise Offline management

It depends on the EMM and what they're using for the DPC. If you're using an AMAPI aligned EMM then my understanding is that the EMM is basically just a console and Google is doing the actual management of the device. In that scenario you would need the devices connected to a public internet connection, or at least with access to all of the Google services. With Custom DPC EMMs you can do many things offline and I have been successfully doing so for years. With fully managed devices, which I'm assume yours are based off the "offline" status, I typically do everything in my power to NOT rely on anything from Google services. They're unpredictable, unreliable, and don't offer admins much visibility or control. I may be a dissenting opinion here on the Android Enterprise forum, but thats my perspective shaped from years of experience deploying these devices.