I am currently running WordPress 3.1.2 on PHP 5.1.6. The minimum requirement for WordPress 3.2 is going to be PHP 5.2.4 or greater. If I keep running WordPress 3.1.2 and there is a security issue will they provide security updates for 3.1 or will I be forced to upgrade my version of PHP so that I can upgrade to WordPress 3.2?
WordPress backports security updates usually 1-3 versions back but they don't promise anything.
The Long Term Suckage theory is:
While I like the theory of LTS, what happens in practice is it covers up the incompetence of IT or developers because they put off small slightly painful upgrades until they get so out of date of trunk (3 years? 5 years?) and you have to go through a giant, painful, screws everybody over upgrade. --Matt Mullenweg
Like how your sysadmin doesn't want to update PHP now that it's 6 years old and 2 major branches behind.
I would point my sysadmin to this thread from the RedHat mailing list from 2009. There are 3rd party packages available so you don't have to compile from source
If the version of php you need is not available in rhn you could use some 3rd party repos like rpmforge, ATrpms or the Remi Collet Repository that is specially made for mysql 5.1 and php5.2.9 under EL5.
I would be more concerned about PHP 5.1 branch security issues than something that might come up with WordPress.
Also found this official RedHat announcement from Jan 2011 RHEL 5 now shipping with PHP 5.3.
No, older versions are not updated.
Aside: PHP 5.1.6 is five years old. Even if WordPress would offer patches for 3.1.2 – you missed more than 100 security fixes for PHP, so WordPress isn’t your main problem anyway.