CentOS purposely does not have a mechanism for holding steady on an old point release.
The point release numbers used for CentOS 6 and earlier generally do not refer to new features, as with most other software. They simply mark the times during CentOS' long release cycles where they batched up the bug fixes and security fixes made to their RPMs and mastered a new set of installation media.
(In fact, starting with CentOS 7, they've abandoned the point release numbering entirely, adding a date code to differentiate new installation media releases.)
If you said yum update on a CentOS 6.0 system on the day CentOS 6.1 came out, the difference between your upgraded CentOS 6.0 system and a fresh 6.1 installation would be very small.
The primary difference between CentOS 6.5 and CentOS 6.6 is a whole pile of bug fixes and security patches. There are typically very few functional changes between such point releases.
It is better to think of yourself as running "CentOS 6" rather than "6.5." The only question is whether you're up-to-date on your fixes or not.
The whole point of using a "stable" Linux like CentOS is that they purposely do not make any functional changes they don't absolutely have to within the major release series. No configuration file formats change, no configuration changes need to be made to use the newly-fixed packages. The software you originally installed with the OS just works better now.
Therefore, I recommend that you do not hold steady on any CentOS point release. Keep your systems up to date! That is how you get security fixes.
There are a very small number of exceptions to the "no new features" policy. Some examples:
They don't seem to keep Firefox held back to an old feature release, for example, probably because it becomes too difficult to back-port security fixes after some point.
Red Hat will occasionally add some new non-breaking feature; they took XFS out of beta status in RHEL 5 and 6 shortly after RHEL 7 shipped, since XFS is the default filesystem in RHEL 7. If you were eschewing XFS in these older OSes because it was considered beta at the time you installed the OS, this effectively means those older machines got a new feature in the middle of the active maintenance cycle. (I believe this happened with CentOS/RHEL 5.10 and 6.5.)
This status change didn't affect your non-XFS filesystems, though, so it is not a problem from a stability standpoint. Only those who were happily using XFS in its beta state cared about the change.
Given that CentOS 6.6 came out about nine months ago now, I don't see why you're waiting on Datastax's approval. Unless you have specific information from them that a particular package is incompatible, I wouldn't keep holding your breath waiting on their approval.
RHEL 6.7 entered beta about two months ago, so it should be appearing soon. CentOS 6.7 should follow in two or three weeks. That means there's a good chance that if you hold off on 6.6, you'll be two releases behind current soon.
If you're still feeling nervous, roll the change to one machine, then two, then four, etc., doubling until all machines have the change.
