I just tried xaRes.end(xid, XAResource.TMSUSPEND) in Oracle and it did not throw any exceptions. The Informix support person had the same comment as yours, if oracle does not fails when passed XAResource.TMSUSPEND then they are not following the standards.
I will be happy to try the code changes in TS. You could send the code to moises.quinto@gmail.com if you prefer.