Most RETAIL drives have 3 year warranties. OEM drives will have 0, 1, 2, 0r 3 year warranties, depending on how much the OEM purchaser was willing to pay. Large companies like Gateway will purchase the drives with NO factory warranty, figuring they will warrant the entire system. Generally speaking, in my experiance, the standard OEM drive will have the same warranty as it's retail brother, but it is never safe to count on it. If in doubt, ASK QUESTIONS!!! And while you're asking, make sure you ask if it's a factory warranty or a shop warranty. Many times there is a 30, 90, or 1 yr shop warranty (return to seller for replacement) backed up with a 3 year manufacturers warranty.
I don't think you should be afraid of an OEM drive, just be aware that there may be differences over and above not coming with cables, manuals, installation software, fancy box, etc.