Supported Exchange target environments only mention Exchange 2013 Release to Manufacturing (RTM) or General Availability (GA) and you are not able to see CU1, CU2, CU3, etc.
Are Exchange Cumulative Updates (CU) supported?
The tool is not tested against CUs. If you see RTM or GA or Service Pack (SP) is supported under Supported Exchange Target Environment, that specific CU of the RTM or GA or Service Pack is supported.
If you do not see the specific SP is supported under Supported Exchange Target Environment, neither the SP or CU of the SP is supported.
