Defrag Raid?

Defragging isn't really needed with OS X. The operating system defrags all files under 20 MBs on the fly.

Yeah, don't bother defragging any kind of volume in Mac OS X. It might even make things slower. In a RAID configuration, just keep available space to a maximum in order to ensure fast operations. If thigns are getting bogged down, check your used disk space on the RAID set.

There is some value in doing a backup, erase and restore.
Moving up to Leopard, I've rebuilt all my RAIDs.

And there is value: you get a backup! But I am not a fan of defragging usually, unless your work with audio or video is improved.

Some files will be - when rewritten - written back as a single unfragmented file.
On some systems, mixed results on latency, searches, and writing updates.