Your RAID will appear to your OS as a regular volume, with regular filesystem, etc. In general, in linux (which I suppose you use, since your avatar you have a pinguim with a brazilian flag) you don't need to defrag.
Your system will do the necessary verifications when you turn it up, linux in general schedules some cheks after x mounts of the filesystem.
The only thing you could take a look at, if your system supports, is the SMART parameters from the HDs. SMART is a technology that tries to warn you when things aren't going well in the HDs. But it depends on the HD model, the OS, the motherboard, the programs you installed to monitor that...