Hi,
I'm running the exact same server in my lab at work (great little beast). Mine is configured with a RAID 1 for the ESXi 5 installation and has been working without any problems for a few weeks now.
Could you help by answering a few questions?
1) Is the server (hard drives) new?
2) If you re-create the RAID 1 drive does the drive return from degraded to online?
3) Do you have any spare SATA disks you could try (even if just temporarily)?
Cheers,