The art department has asked me to add custom data to FBX files at export time from Maya.
(Custom camera and material animation data)
This is possible with the Autodesk FBX Extensions SDK.
Is there a way for custom fbx data to be imported into Unity ?
Yes there is, but as it is intrinsically custom you would need to write an asset post processor to tell Unity what you want to do with that data:
As we don’t have direct counterparts to all the functionality in Maya (many features designed perhaps for an offline rendering target, rather than real time platforms) then it may be difficult to implement what you want to do with that data, for example the kinds of material animation that Maya is capable of may not translate directly to UV animation or Material colour animation curves available to you in Unity. So the short answer is yes theoretically, but the long answer depends on exactly what you want to do with that custom data and what resources you have to do it.