Yes, OpenCPN recognizes an AIS SART, but only as "normal" AIS. I don't think it is possible to adjust settings so an alarm goes off when a new AIS SART comes within range as a result of a mob incident. So it's no on the second question.
Expect this this change in the future!
There is a feature request for this in the tracker. FS#335 : AIS SART not supported
OpenCPN needs a special symbol for an AIS SART and an immediate alarm as soon as an AIS SART comes within range.
Kannad has supposedly put a text string into the AIS message stating that it's a mob. Can anyone confirm if this works with OpenCPN?