For what it's worth, we just bought some mxeIII's with raid and ssd's and it's been fine so far. (installed earlier this year)
I'm not a certified Mitel tech, but I'd have to assume the guys that installed mine did so according to the official method. Perhaps there's a certain chipset or something that's mitel-certified or something?
Disk 1 id matches
  Current Model Number  : LITEON CV1-CB64                         
  Expected Model Number : LITEON CV1-CB64                         
  Current Serial Number : 0029321014EL        
  Expected Serial Number: 0029321014EL        
Disk 2 id matches
  Current Model Number  : LITEON CV1-CB64                         
  Expected Model Number : LITEON CV1-CB64                         
  Current Serial Number : 0029321014EE        
  Expected Serial Number: 0029321014EE     
(incidentally, I use those same drives in some 200 pc's and they work fantastic.)
-dg