If you have the correct HDD caddy for the multibay and can ascertain that the drive that goes into it is a plain vanilla 2.5" drive IDE drive, then you can simply plug in whatever disk that takes your fancy - and again confirm whether it takes 12 or 9.5mm high disks (or either).
If, however, the caddy requires a different (proprietary) interface to the HDD, then you are stuck with the OEM version.
I suspect that the latter is unlikely in an IDE setup.
The only time I have seen this has been with hot-pluggable SCSI disks - not really necessary here!
SD