This answer is an update on the current status about the question.
As of Gen8, you cannot put non-HP disk into a HP server, as the HDD trays became intelligent.
The trays communicate with the server so the server can log what HDD (with what serial number) you put into the server.
HP has some marketing jibjab about how this solution increases stability and whatnot, but this primarily exist to block attempts to get support on a non-supported disks by raising a support ticket with a supported server's serial several times (like having N storage JBOD, one with support, the others without support, and reporting all failed disks through the supported JBOD).
The above example is a direct attempt to avoid support fees, but this violation of support agreement can happen in good faith.
By default a standard or nearline disk has 1 year support and enterprise labeled disks have 3 years, but buying a Care Pack to a server increases the support time for all the disks inside it, to 3 years.
Let's say you have a storage (A), with the default 1 year support, and another storage (B) with 3 year support. In the 2nd year a disk fails in storage B, and you were to replace it immediately with a disk from Storage A (then have support for that failed disk, but put the changed disk on the shelf). If the replaced disk would fail, you couldn't have it change by HP support, as this disk had only 1 year support. But you would be raising a support ticket to storage B, which has 3 year support, so it would look that all the disks inside have 3 year support.
These smart HDD trays, along with the server log now give HP a tool that can detect this and HP can reject the support.