If you are using Poser Pro 11, you can specify to import the OBJ as a Poser-size item, then you can see it. If it has normals reversed, and the Parameter dials tab has setting to hide backfacing polygons, it may also cause the imported item to appear invisible in preview textured mode. As already mentioned, huge size would make it un-observable because the cameras would be inside the object. (I also find that if I point to the wrong item during export from my modelling software, I get a OBJ without any geometry.) Uhm, I have also had the odd experience that in some cases, if you don't export an OBJ with Material, the item is invisible in Poser scene.

Eternal Hobbyist