Can I use an Endpoint Policy Manager Cloud installer and license for domain-joined and non-domain joined machines?

Yes, you can install the Netwrix Endpoint Policy Manager (formerly PolicyPak) Cloud Client for all Windows machines: non-domain joined and domain joined. That being said, the opposite is not true. You cannot install the on-prem CSE and have it connect to the cloud service. You need the cloud client to claim a cloud license, and that can be used for either/both Domain Joined and non-DJ machines.