the short answer is, you should. EPDM 2013 will not be able to ready any of the new stuff in the 2014 files. and may not be able to read them at all (to find file references and such).
but you should still be able to check-in and check-out the files and send them through work-flows.
(note: this is how I understand the relationship - but we are still on 2012 )
As documented in the SolidWorks 2014 release notes at the following link, using SolidWorks 2014 without the matching Enterprise PDM version is NOT supported:
I hope this helps,