I've found to my chagrin that Mettle FreeForm does not match up with any other 3d layers in the same composition if I move the camera. It will respond to the camera, but in a manner wildly misaligned from the rest of AE 3d space... is this normal??
No, it is not. The integration should be flawless. The one thing I can think of is if your other 3d layers/objects are positioned before you create the FF layer. You need to position the FF object in 3d space using the plugin controls to match the x,y,z of the plane you are trying to match it up with. It may be that you need to reset position on all layers to "0" and re-position everything again.