Technically, yes you could use FBX to drive bone locations in a Spine skeleton. We don't have tools to do that though. You would probably want to define a camera and project the 3D points to 2D from the camera's perspective.
How useful it would be is somewhat questionable. Animating in 3D is mostly "realistic", you don't need as much "faking". You can view your skeleton in 3D from many angles so generally it has to look good from any (or at least multiple) angles. You mostly animate all the real movements and that lets you do some nice things, like retargeting animations to other skeletons.
In 2D everything happens on the same plane, so you effectively only view it from a single angle. To get depth and other effects, you move the bones however is needed to achieve the look you want. Often that doesn't map well between 3D and 2D or vice versa. Since you haven't really defined the true movements, only the movements necessary to get the look you need for the one particular angle, it also makes retargeting the animation to another 2D skeleton less useful.
That's just the nature of 2D animation. 2D is easier to animate but the animation data isn't as "good" as your painstakingly crafted 3D animations.
