With UR#5 for SCOM 2012 R2 SQL Server 2014 is supported. At least, sort of supported. Please keep in mind there are some ‘challenges’ to be addressed.
Want to know more? Read this posting on the SCOM Engineering blog. My own two cents: Only use SQL Server 2014 for SCOM 2012 R2 UR#5 when it’s a hard requirement. Otherwise use SQL Server 2012x.