Hi,
You can verify as per the following matrix for the recommended version of IOS
http://www.cisco.com/c/dam/en/us/td/docs/voice_ip_comm/uc_system/unified/communications/system/Compatibility/CSR-Compatibility-Matrix-InteractiveHTML.html
However, in case of IOS backward compatibility works with cucm so even this current version would work , however upgrading to the recommended version gives you more bug fixes and new features.
Manish