The Breen have been given some pretty conflicting attributes in their backstory, but this much seems to be nicely supported, yes.
In "Hero Worship", the Breen are said to practice boarding attacks. In "Indiscretion", we learn of their slave-capturing antics. The energy weapon is a pretty natural continuation of that story, although one wonders why this ideal piracy weapon never became infamous amongst its victims before the big war. Would the Breen have had enough discipline not to use it for piracy? They certainly didn't completely silence all their victims, as some
rumors of their habits and methods circulated in the UFP.
This would suggest the weapon was a new addition to the Breen arsenal of piracy and boarding attacks in the late stages of the Dominion War...
I wonder if any of the ships at Chin'toka were boarded and captured?