If they have "JBOD" mode, then you can access the drives individually, although you can RAID-0, 1, or 10 yourself within OS X using Disk Utility. Otherwise, they will probably have a hardware RAID in the enclosure and will appear as a single drive to OS X. The enclosure will have multiple eSATA connectors for the drives, and present a single pass-though (usually) Thunderbolt interface to the computer.
If you want the flexibility of a Thunderbolt JBOD enclosure, I like the OWC "Thunderbay IV" (or the new TB2 "Thunderbay 4"). Both are available as bare enclosures, or already configured with drives (and SoftRAID-5 if desired). Fast and quiet!
Do a search on Amazon and you will find all price ranges of enclosures to do what you want. Most will have eSATA, USB 3.0, and FireWire interface choices. Some will be Thunderbolt. Read the reviews, some will be quite noisy and may be objectionable to you.