Looking at those renders, there could be two reasons that the seam is visible. One is that the vertices are not being welded when they are exported by Alibre, resulting in duplicate edges along the seam, or, more unlikely, a deliberate Phong break is being applied to that edge. Either way, the Phong smoother is stopping at that seam. Somehow, you have to weld all the duplicate vertices so that there is no obvious break that the render engine can see.