They have been released out in the open, recently, relieving the scouts from having to be overly agressive and trigger happy, which they aren't really built for, as far as I can see...Only encountered them inside the Maelstrom, launched from the Titan so far - but i presume their Hunter class means they will be venturing further out & about…^
And I guess this has been done to enable the Scouts to act as Revenant-carriers...