Thats I kind of cool idea having classes have to work together in order to use certain abilities but I dont think Operatives need anything else they already have a wide variety of offensive abilities not to mention if they could get that close why not use the backstab ability? IMO from what we know sounds like they may be OP considering they will have a perfect disguise which only other Operatives can spot out. There should be some sort of clue for anyone to spot them out wether it be slight dis coloration, not showing up on mini map, crosshairs turning red, ect for anyone to have a chance to make them out if they pay attention because you shouldnt have to rely on one person on your team to tell you if there is a sabotuer in your midst as well you wont really have to time to watch there behaviors like people keep saying. This game is going to be fast past close quarter combat they already stated that. That is one the reason there is no sniper class and sniping is not integrated into the game so your not going to have the time to sit and watch people behavior on your team when your in gun fights ect most the time. But I guess we will see how it all works out when the game is released I'm sure there will be something for people to be able to tell if there is an enemy operative among you since the game is really focused on balance.
From what I understand about operatives there will be several ways to tell that they are in fact enemies in disguise.
The first way is the soft collision that will be in the game. Teammates will be able to pass through each other and only be softly pushed away from each other. Enemies, however, will not be able to pass through each other. If you collide with a person who looks to be on your team and can't pass through then you've found an operative.
Another way would be their behavior. Even if you did get into a gunfight they could very easily give themselves away if they are not careful. If someone who looks like a teammate runs from the enemy side of a firefight right at me and does not draw any fire, I will probably get very suspicious very quickly.
A third way is the disguises that they have to use. From what I understand, operatives have to disguise themselves as one of the enemies that has recently died. So if you see two of the same guys running around, one of them is obviously a disguised operative.
Yet another way to tell if a person is an operative is the SMART system. I am not so sure if this will actually will be the case so the first three points will be the major identifiers of operatives. This also sort of relates to my third point. When an operative disguises as another weight class, their SMART moves will be unaffected according to what I have heard. Therefore, if you see a heavy jumping off of walls and doing other acrobatic maneuvers, then you have found an operative. Somebody correct me if I'm wrong about this.
So all in all, the only thing you need to do to catch most operatives is to pay attention to those around you.