The Intel's Linux NVMe Driver Reference Guide mentioned building the driver for linux kernel 3.10.0 and above.
nvmexpress.org mentioned that the working Linux driver is included starting from kernel 3.3
http://www.nvmexpress.org/resources/linux-driver-information/
Since CentOS 6.5 and 6.6 is using kernel 2.6, most likely whatever included driver (backported?) may not function properly.
In your case it would be better for you to use CentOS 7.0 (kernel 3.10) for best compatibility.