This is how the FBI defines 'suitability' of hair samples:
http://www.fbi.gov/hq/lab/fsc/backissu/jan2004/research/2004_01_research01b.htm
The lack of suitability could mean there weren't enough hairs of a 'known standard' for comparison. Maybe there were none. We don't know.
Had Cindy handed in the brush she used "only for Caylee", all of the hairs would have been identical and would have provided a 'known standard'. Cindy messed up, and was caught by her own written admission.
Whether the FBI is able to definitely identify the 'death band' hair as being Caylee's using other samples of her DNA is not known. The test results released were those of a hair comparison.
There are many forensic results not yet released - the maggot tests, the tests on the shovel, the composition of the stain found in the trunk, whatever it was that Dr. Lee found...