In my Bamboo build, after checkout I run the tests with JUnit output and collect the resulting XML with a JUnit parser to process them. I checked the generated XML and it seems to me that the "failed as expected" tests in the XML output look the same as regular failures:
<testcase classname="[Warning] Broken: [Item]: behaviour" name="behaves well" time="0.032112">
<failure message="!true" type="CHECK_FALSE">at c:\test\src\automatedtestgeneration.cpp(612) </failure> <failure message="!true" type="CHECK_FALSE">at c:\test\src\automatedtestgeneration.cpp(612) </failure> </testcase>