That’s not so, I haven’t used Jeremy’s A.R.T Maya tools at all and I’ve managed to import many characters with additional meshes skinned to the main skeleton. What that looks like in your image is that you’ve not rigged it properly in Maya. It’s difficult to say without seeing your Maya scene file, but the armour hasn’t been bound to the bind pose properly!
All the A.R.T tools are for - is an automatic pipeline for rigging, the don’t posses a magic solution to rigging. So whether you use Maya, 3ds Max or blender, the tools aren’t the problem.