If you're server is running a RAID 1 you could remove one of the disk sets, run the IDR test on the second set and then boot back to the first set and rebuild the RAID onto the first set. Just make sure you're very familiar with the options of the RAID BIOS.
If you don't have RAID1, to test if IDR works with the NAS, you can try & restore to a client PC. The IDR process may work, but the PC probably won't boot after IDR though.