You're right that you can at least use Perforce as the underlying database, but "worked great" is subjective.
The concept of version control is much more integrated into the UX of the Unreal tools, with things like visual diff/merge support for assets built in.
Additionally, one of Unreal's killer features for scaling collaboration up with larger teams is the idea of editing a map in multiple distinct layers which are composed at runtime. This means you can have someone working on audio in the audio layer, someone working on collisions in the collision layer, someone working on lights in the lighting layer... all in parallel. If you tried that in Unity, all you'd end up with is a binary blob with a merge conflict, and n-1 people having wasted their time.
That's an excellent feature. the scenes in unity are binary and not merge-able. That feature alone left me considering other options when I was looking at game engines.
I am legitimately surprised they're using a binary format for scenes. That is very anti-source control in general. The only binary blobs in the entire project should be assets (e.g. textures, sounds, etc). Everyone loves to whine about XMl, but I'd happily take XML for scene layout over a binary blob.
Scenes and prefabs have been able to be saved in a text format for a while. That said, they were still effectively unable to be merged in all but the simplest of situations for reasons I don't fully understand.
Hopefully this was improved in Unity 5. One of the buried release notes mentions a new merge tool for scenes and prefabs in the engine.
The concept of version control is much more integrated into the UX of the Unreal tools, with things like visual diff/merge support for assets built in.
Additionally, one of Unreal's killer features for scaling collaboration up with larger teams is the idea of editing a map in multiple distinct layers which are composed at runtime. This means you can have someone working on audio in the audio layer, someone working on collisions in the collision layer, someone working on lights in the lighting layer... all in parallel. If you tried that in Unity, all you'd end up with is a binary blob with a merge conflict, and n-1 people having wasted their time.