In my experience, it works like this:
If you can sculpt, you may not be able to draw.
If you draw, you can definitely learn to sculpt.
I've seen this for years -- sculptors and modelers that are terrible at drawing but can render forms in an excellent fashion. Anyone with a solid grasp of drawing perspective and/or organic forms such as the human body are quickly able to model equally well (once getting past the technology).
That said, if you cannot draw, you can definitely learn to be good at 3D.