Magento2 requires PHP 5.5 or PHP 5.6
Frustratingly it will 'mostly' work on php 5.3 - it is just a few functions that will not work, or they work but not as expected - so it will appear to work fine.
Mac OSX runs PHP 5.6 - so if your testing things locally you will end up with different results then on the server.
Nexcess will install just about anything we want on a dedicated server[sip4.. or sip5...] - the one limitation is that the installation will generally apply to an entire siteworx account. IE we can run php 5.3 for all the current siteworx accounts, and PHP 5.6 for a single test siteworx account.
So for Magento2 testing, you must create a new siteworx account, it must be on a sip4 or sip5 server, and you must open a trouble ticket on the portal, https://portal.nexcess.net/
Subject line: upgrade PHP to PHP 5.6 for siteworx account ....
For service: the sipX account
Body:Please install PHP 5.6 on sipX.... only for siteworx account XXX.
I like to make absolutely clear that this is not for every account, just the testing account.