I suppose we can use a combination of the changes you propose: bump up the ORB defaults a little bit, cut back the stress test, or even alter the test execution based on the target (JTA vs JTS) doing some property checking.
Also setting jacorb.poa.queue_wait=on may reduce the number of Threads we need in the pool to keep up with the test, which in turn may reduce the need to mess with -Xss and ulimit in order to avoid the 'java.lang.OutOfMemoryError: unable to create new native thread' problem.
I took a look at the test case in question.
The success/failure has a lot to do with timing (which should be fixed) and the parameters used for the setup. The JTS setup shows > 10x longer running period than the JTA counterpart.
So I would say that the *StressTestCase should be excluded for now from the run - and we should look into how better test cases could be implemented in this area.