RAID 10 would offer them the ability to lose 1/2 the drives for a smaller performance penalty than losing 2 drives in a RAID 6.
No, two dead drives in the same pair and the array is toast on raid 10. Two drives and the RAID 6 they described survives.
One of these rack units can survive at least two drive failures, but can survive zero power supply failures. I've pitched many more dead power supplies than hard drives. If the power supply dies during a write (RAID + no battery backup + two parity drives), consider the array corrupted.