I just recently learned here http://layersmagazine.com/after-effects-cs4-3d-effects.html#more-3027 that you can import a 3d object into AE4 and above if the file is in a 3d PSD format.
My question is, can I get that object to cast a shadow onto a floor that I create using an AE 3d layer? So far I haven't been able to. Nor have I been able to even get the 3d object to intersect with the floor.
No and no. Since it is an intra-layer effect, it suffers the same limitations like any otehr pseudo-3D in AE.