if you want to subdivide an imported model you need to create the polygroup structure. In the future we hope to build this structure on import but for now you can define it in couple ways. One method is by setting all the edges in maya to Hard. Then when importing the fbx turn on import normals. Then you can generate the polygroups with the oconversion mode set to “from hard normals seams” this should give you a polygroup set that represents your original edges. Assuming you have a quad model it should be compatible with the subdivide tool.