Naturally, but it also depends on player level (and some purely random factor).It's probably related to the maps you end up playing in Co-op. I have been assigned the same maps rather often.
There are at least 3 maps I encounter chameleons almost every single time. Bryce Canyon, where you saw it once, for example is one of them.
There are some variation in enemy spawns but they pretty much spawn from the same known locations for me so far.
Spawn points are fixed, whether they are used, what spawns and when they spawn changes.
BTW, knowing what's going to spawn where is very valuable if you are a spec ops with decent level. In any case, I can guarantee you guys haven't played most of the configurations yet.