By default, the Vanishing Point grids are invisible when viewing an image in the Photoshop document window, even though the grids are preserved in the image and appear whenever you launch Vanishing Point. Grids can be rendered so when you finish working in Vanishing Point, they’re visible in the Photoshop document window. The rendered grids are raster not vector.
The Render Grids To Photoshop command must be chosen for each Vanishing Point session.