You sure do seem to get a lot of hard luck don't you? And all with OCUK, I never have known anybody have so much bad luck with one supplier.
You know, it's quite odd because in all the years I ordered stuff from OCUK I never experienced one case of bad packing.
And I thought you'd stopped using OCUK
Are you sure the number you're looking at is the serial number? If you're positive it is then yes, every hard disk serial number is unique.
Did you take a picture of the hard disk you returned or just noted down the serial number and perhaps some other details?
If the hard disk works well initially then it's unlikely to fail because of damage sustained in transit, any faults would probably be immediately apparent.
Also, Samsung give a three year warranty I believe and it's easier to deal direct with Samsung for an RMA than it would be to deal with OCUK, this is common practice. You would have to pay postage to send it though if you dealt with any hard disk manufacturer directly, that's just the way it is.
Myself, I honestly couldn't be bothered with all the kerfuffle and would just use the hard disk.
Is it going to be used for an OS or storage?