I made a model in Mudbox 2012, exported the FBX, imported it to Unity but there’s nothing. i can open it in Maya, and its works fine, but it’s invisible in Unity. no mesh.
Unity 3.4 is based on FBXSDK 2011.3.1. Try setting FBX format to 2011 when exporting from Mudbox.
Otherwise Unity should import FBX from any software. If it doesn’t - raise a bug.