The COBOL client libraries are supported on z/OS version 1.x. The Client library is sold separately and does not come as a part of the standard EMS software. It is available at download.tibco.com . The package also provides COBOL sample programs.
It is mentioned in TIBCO Enterprise Message Service C and COBOL Reference->Chapter 1 Introduction->Overview that:
TIBCO Enterprise Message Service Java API implements (and extends) the JMS 1.1 specification. TIBCO Enterprise Message Service C API closely mimics the Java API. The EMS COBOL API brings the power of EMS to z/OS systems. Its entry points are parallel to those of the C API, with identical function names and similar parameters.