The Shared Java Services Libraries is a neat feature for the 2.2 Xcp Documentum but is problematic in this specific case.
A little bit of background: I have to make a migration from a 2.0 Xcp project to the 2.2 version. I started a new project and gradually added all the artifact, custom widgets and sources, since a migration from 2.0 to 2.2 is not possible directly.
The java modules from the old project are found in the Artifacts/Java Modules in the form of .javamodule files. Each .javamodule file has a list of implementationJars where is specified each content path of the needed jars. This is a good thing since I have several .javamodule that use the same libraries but with different versions and I can control what libraries will be used to that particular .javamodule.
When I try to do the same thing in Xcp 2.2, all the jars are saved in the same location (that's why is 'Shared Java Services Libraries') and in the .javaservice files that are created automatically (the 2.2 .javamodule equivalent) I can't specify which jar library should it use. Can I 'unshare' the libraries or is there a .javaservice notation that can be used to specify the particular jars libraries for that .javaservice?
Personally I didn't work on project that used designer 2.0 or 2.2, but from what I see in Designer and Release Notes things didn't change from 2.1 -> 2.2.
When you create new Java Service you need to specify primary class for it. If you have available Java classes to select for class to your Java Service then you can skip adding new jar. Otherwise you need to provide jar with class that you'll select as a class for your Java Service.
Once you have your Java Service you are free to use it in processes or anywhere else it is supposed to use.
When you open your *.javaservice file you'll see that it has primaryClassName where it holds the value you specified for the class used by your Java Service.
So the answer to your question would be: every jar you added to the xCP application can be used for any Java Service. I recall that I had numerous bugs when designing application and extensively adjusting Java code used by Java Services but I hope EMC engineers fixed it in new versions. If you'll have problems with it return on SO. :)