A unit whose only real use would be to kill dead players?
It would be annoying for the Resistance players when the Overwatch was using this unit well, and it would be annoying for the Overwatch to use the unit well. He'd need to keep the Cremator out of sight so that it wouldn't die too soon while at the same time try to kill the Resistance players with his other units, then quickly bring in the Cremator to clean up the bodies, take him out of sight again, and so on. If the Overwatch spawned more than one Cremator, his total firepower would drop too much. I don't see this unit as a fun gameplay element, and don't really have any ideas how to make him into one.
Also, if the Combine didn't think the players were already dead, they would just finish them off with bullets. You don't need an organic matter dissolving hose to kill someone crawling on the ground. But letting the normal Combine soldiers to finish off the revivable players wouldn't be a good gameplay element either, because then there wouldn't really be much point in having the revive ability to begin with.
Reviving is still a bit incoherent because it brings you back in full health and ammo, making dying and getting revived again sometimes be a benefit for the Resistance. This needs fixing, but there are other, better ways to make it work as it should than by introducing an entirely new gameplay element to clean up the mess (with a large hose).