We're currently setting OneWayProcessorInterceptor.USE_ORIGINAL_THREAD to true for EJB3 endpoints, as that's required for proper authorization in the ejb container. We should actually set that by default in the deployment bus, so that any deployment defaults to using the original thread for deailing with oneway message.
The reason for this is also performances: when a new thread is used for dealing with a oneway message, the message needs to be cached which takes time and memory. Moreover, the user should actually be tuning the web container thread pool to control thread usage when serving ws requests.