Urban territory as such offers plenty of cover. Most missions take place in places filled with piles of junk, walls, ruined cars etc, so this is plausible. That leaves the other aspects - what is feasible by game engine, and balance.
How do zeds find the survivors? Presumably by sight, hearing, and perhaps, smell. Invisibility as concept requires defining what it is to see and be seen.
* Sight: defining line-of-sight so it makes sense to a computer is not obvious. I have no idea how Con has done it, but based on zed tactics that I see when they attack my compound, they seem to pick the shortest unobstructed route to a survivor, so the game engine is aware of where the shortest unobstructed path goes. (Some, but not all, zeds also attack barricades, which once made for a really strange battle where the last zed just stood there, while all my survivors were inside a box of sandbags, ready to perforate anything that gets in range.. but unable to get to that last zed.) The same can be done on a map where all the see-through, shoot-through components of the map.. sandbags, low shelfs, windows, iron grates.. are considered passable. If that path between A and B is as long as the actual shortest path between A and B, and if the path is short enough, it is possible to see, and shoot, between those points. Normally maps are small so visibility is not a problem, but at night, or in a fog or rain, sight range could be shorter. Less time to shoot at the zeds you do see.. but many zeds that don't see you at all. If this is so, then the invisibility would mean that the zeds need to be really close to see the ninja type.
* Hearing: this depends on activity, and follows a map where shoot-through parts of the map are considered passable.. sound does pass over a kitchen sink, after all. Every action has a noise rating; if you're close enough, you can be heard. No LOS needed.
* Smell: I suppose zeds can track a trail be scent, and smell a survivor that is close enough. Once a zed attacks, it will keep attacking until either the zed or its prey goes down. At that point, it's not possible to outrun it and hide. Or should it be?
So, if the senses that zeds hunt by are defined, then sure, the concept of invisibility makes sense. I don't like absolutes though.. so I would make it reduced visibility rather than complete invisibility. Camouflage gear, perhaps, rather than Book of Invisibility.
In PvP, I see this as more of a defensive thing than something that attackers do. Hide the defenders from the attackers. Camo netting on barricades perhaps. Attacking a compound is fairly easy anyhow, as the attackers can actively adapt, whereas defenders only have the advantage of terrain. Would be fun to have some added tricks up my sleeve for PvP defense, making the compound a more difficult puzzle for invaders, but that's another topic.