I believe there is at least one UL listed system that uses wireless technology, in place of that third wire, to interlock the units. If nothing else, this makes it easier to add such detectors to existing buildings, and place them on different circuits. (Some homes are large enough to push the limits of one circuit).
Assuming the system was listed for such use, I would have no problem with it. Code only requires one tripped detector to result in all of them sounding off ... Code is silaent as to how that is accomplished.