My answers to your questions (by number):
1a. Are you comfortable with a short warranty for your money?
1b. They are probably exactly the same as the retail versions, BUT know if they have been remanufactured or not.
2. Not sure about firmware. I personally have never heard of updating a drive's firmware, but I guess anything is possible. If at all possible, contact Dell or Quantum for a good answer. Might even be in the faqs.
Generally, price difference in OEM vs. Retail is made up with who provides the first level of support. OEM would be cheaper at the wholesale level, then they would mark it up to make up for selling and supporting the device.
Notes about RAID: Be sure that the drives are identical for the best results. Initio makes a killer lvd card. (I'm using the Miles2 in my G4 connected to Cheetahs.)
Good Luck!
------------------
-Keith
-Whatever you do, do the research.