Our institution has decided that they wanted to test Intune (ConfigMgr Hybrid) without adding our Domain to the Intune portal and sync domain account to the default (domain.onmicrosoft.com) instance.  I am having a difficult time getting a number of things working (Device Enrollment, passwords to sync via AAD Sync, etc.) and believe that is has to do with the fact that we choose to not add our domain for the initial tests but am having difficulties proving it.

Can anyone tell me if this test Design would be troublesome? Would having your Directories Domain added to the portal provide a cleaner test environment?  I need something to tell the powers that be that we need to actually add our domain to have a good test environment before they are willing to forgo these tests.

Thanks for your time.

Technically speaking you don't need your public domain name configured, but it would indeed give you a cleaner production like test. When you're not using a public domain name, you do have to configure the domain.onmicrosoft.com as primary UPN for the synchronized test users. Once that's discovered by ConfigMgr you can succesfully synchronize licensed users, as the UPN will now match with the users that are synchronized via AAD Sync.

Also it's no big deal adding your domain. You can get it removed again if you decide not to proceed.

To Gerry's point, you're going to find this much easier if you proof your domain. You can always remove it later.

The challenge you're going to run in to here is SCCM is trying to match the UPNs in AAD to your on-prem users so it can match them up. When the UPNs are mismatched (as-is going to be the case here), you're going to run in to challenges.