If a UUIDv4 is used, then yes, I'm convinced it will be random to within the amount of entropy the system provides. If another UUID version is used, I'm extrem

If a UUIDv4 is used, then yes, I'm convinced it will be random to within the amount of entropy the system provides. If another UUID version is used, I'm extremely wary. MAC addresses are explicitly not unique. Worse, there are plenty of bargain mfgs that make cards all with the same MAC. There's a story of a local college that ordered several hundred cards for workstations and discovered every single one had the exact same hardware MAC. Large orgs will spot this easily, but there could be hundreds or thousands of individuals that never tried connecting the same bad cards on the same network segment. In practice, you can usually depend on it to be truly unique. But there are several failure modes that you absolutely need to be aware of if you plan on using this in production.