Velociraptor, OEM and otherwise

I bought a Velociraptor at Micro Center when they were still available. Wonderful drive, I wish I had bought more.

Many used ones are available for sale at well-known Internet sites. Some are listed as OEM, whether Lenovo, Dell, or HP. In the case of SSDs, OEM always translates to firmware with different rules, with the most common one being that manufacturer firmware cannot be installed.

Unlike with SSDs, OEM Velociraptors do not appear to include the name of the OEM on the label. Is there any way to distinguish between retail and OEM, or did Dell and the others simply buy large quantities of the same drives which were available for sale at Micro Center and other outlets?

Can OEM Velociraptors be upgraded with WDC firmware? Is this true for some OEMs, but not for others?