There's little practical difference between a 'retail' or 'OEM' HDD for consumer systems. For the same model, its the exact same disk drive, with all the relevant internal parts needed to make it function. In general such drives are primarily marketed at system builders (who'd rather get a padded box of drives with just the necessary packaging).
In general OEM packaging looks like this
You have a drive in a sealed bag, and that's it. No SATA cables, manuals or anything else.
Drives absolutely do not ship with exposed platters
Depending on the type of drive and the SKU you may get some additional literature (like manuals), a sata cable, or in the case of some SSDs a 'migration kit' that would let you hook up your drive over USB, image, and swap drives.
I'd also add if it is a prebuilt PC, or server in some cases the replacing the 'OEM' drives that come standard with it have your own drives (OEM or otherwise) may void the warranty. Some may also have specific firmware versions or be branded to the system builder.