Yes it is the new event added in
DM-38097 which will be part of ts_xml 16. It sounds to me as if your new rule should probably write those events instead of reporting traditional alarm severities. But I suggest talking to tribeiro about it.
Regarding blocking calls to the butler: no Rule is allowed to hog the event loop, as that can render the Watcher unresponsive and unable to do its job. Doing anything with the butler (including creating it) must be done in a background thread unless you are 100% positive that it can never take more than a fraction of a millisecond (preferably much, much less). If I was writing the rule I would perform all butler operations in a background thread unless it is something intrinsically trivial and guaranteed to be very fast.
As to "extra failures" I was just wondering if you had more than one level of severity in mind. But if you use the new event instead of alarm severities, it is not important.