From the horse's mouth: http://answers.unity3d.com/questions/9675/is-unity-engine-wr...
And I don't doubt that alot of devs use Unity, it's most likely the most popular game engine. But it's still a C++ project, despite the languages used to script game events...
I realise that there are no doubt a number of custom C++ engines out there with embedded scripting languages but push for multi-platform mobile games has caused an huge shift towards Unity.
Maybe I'm moving in the wrong circled here — but anecdotally all the people I know making iOS & Android games are developing in Unity.