Standard Maya animation workflow involves multiple animation files referencing a single rig file. When Maya does this it prefixes all nodes in the rig file with a namespace, including bones and meshes.
This means by default, animation files and rig files have a hierarchy mismatch when exported to FBX.
It would be good if the FBX importer had an option to remove these namespaces from the files' contents.
So for example the imported object in Unity would be called "LeftUpperLeg" instead of "Male01:LeftUpperLeg".