BethC -- Yes, if you configure the environment for registered devices only, then from an Apple perspective you essentially prevent devices that are not Apple Business Manager synced (and/or pre-registered). If you unenroll a device, it should still be "registered' and you can then re-enroll via the Hub (although it will no longer be enrolled through Apple Business Manager).
That said, there are a few macOS nuances that lead folks to doing wipe/reloads:
To answer your last question, generally speaking wipe/reload should be your last resort when troubleshooting macOS. You should be able to gather hub logs (for hub functionality), a sysdiagnose (preferably with the Apple GSS debug profile downloaded/enabled from developer.apple.com) for general macOS functionality (mdmclient, appstore, storedownloadd, etc), and details from the "troubleshooting" tab in the device details view.
I hope that helps point you in the right direction!