I myself just tried the 6.6 package for the first time on a new machine.
Some details:
# uname -a
Linux <blah> 2.6.32-504.1.3.el6.x86_64 #1 SMP Fri Oct 31 11:37:10 EDT 2014 x86_64 x86_64 x86_64 GNU/Linux
package - MLNX_OFED_LINUX-2.3-2.0.0-rhel6.6-x86_64
What I got in the log:
error: Failed build dependencies:
opensm-devel is needed by ibutils-1.5.7.1-0.10.g385f871.x86_64
Cheers