Did you merge the vertices (Edit Polygons --> Merge Vertices) after combining and snapping? It's been awhile but I think what I did was a combine to make the body and arm one object. Next, I used the split poly tool on the body to match where I wanted to attach the arm and deleted to make a hole. Then, I snapped verts on the arm and snapped them to the matched verts on the body. Finally, I just drag selected over each pair of verts and merged vertices.

Hope this helps.