Is it possible to upgrade the Mainframe Datacom Server component to the latest release and keep the PC or client users on the previous release?
The compatibility between different versions of the PC client ODBC and JDBC drivers and the mainframe versions is documented in section Version Compatibility Matrixes.
This matrix includes the compatibility of Datacom Server 15.1 and the compatibility of earlier releases.
More information can be found under the documentation "README for CA Datacom Server 15.1"
Also, review the readme.html file that is installed with the PC client software (Windows only).