Well, it should be, providing nothing on your scene absolutely relies on anything from their scene (ie. joints in a referenced scene being skin weighted to meshes in your scene, or objects in their scene being parented to objects in your scene).
As long as your stuff doesn't connect (I mean "connect" in a heirarchical or node-based way) with any of the reference's stuff, it should be fine to have as many references as you want.
If you do need to have stuff from the reference scene interacting/connecting with yours (or vice-versa), then you need to make sure that you know exactly who is working on what scene, what reference, what they are doing to it and when it will be committed.
If someone makes a major change in a scene that you're referencing and relying on, then you need to know what it is and how it will affect you.
As long as you keep on top of this, then you should be fine.
Basically there should not be many issues if, say, someone is modelling a single house and you're making a large scene using multiple copies of the house reference, as long as they have a "control group" transform node whose name never changes, containing all the stuff you need to move around. Since if you are referencing in and moving around houses from the other scene, if they change the name of the node that you've been editing, then the whole thing will fall apart. Similarly if they place another different node above it in the heirarchy then strange things may happen (or may not).
Basically you will need to keep a very tight rein on what is being edited in each referenced scene, and make sure no drastic name changes of important nodes take place.
If you're not editing anything in the referenced scenes (not even moving/rotating/scaling), then that is the ideal situation.