Basically - and as far as I know - WorkManagers are a mean Ibm introduced to allow a certain degree of parallelism within Java EE components (such as
servlets, EJBs), since it' strongly descouraged usage of spawned threads within a Java EE context.
With recent WAS 8.5.x and support for EJB 3.1 with parallelism required by the specification via @Asynchronous annotation, I think you'll need no longer
to use WorkManagers, even if I suppose they're still used under the hood to implement actually parallelism and asynchronism.
For example, I suggest you to search for example on IBM website.