I have not used that plugin myself, please be sure to reach out via the user list for geoserver questions.
There is of course commercial support, many organizations (including my employer) are reachable for one on one support: http://geoserver.org/support
One tip I can offer is to find the code in geoserver github repository, and look in the pom.xml to see if a developer or company is associated with the work. You may also look at the history to see if specific groups have a knowledge of the codebase. This is very good research to do when choosing commercial support.
In this case https://github.com/geoserver/geoserver/tree/main/src/community/jms-cluster is a community module, so it is being shared in the hopes of collaboration with other developers such as yourself. You may also wish to look at the test cases for a working example of how to configure.
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Jody Garnett