Snap is overrated! Why not manually place the corners? If you have thousands of curved sections and absolutely need snaps, try importing the file into a 3rd party software to inspect it. I am not certain how PlayUp sets up pivot points etc, so it may be an issue with the exporter. Export the mesh from CryEngine, in the File menu there is an option to export selected geometry as an OBJ. I'm curious to see how a mesh looks after its exported from SketchUp
I mean, if it is absolutely critical that you have snapping...you could try a different route for importing:
-Export an OBJ from SketchUp with the plugin (make sure you have the correct material folder afterward)
-Import the OBJ into Blender or 3dsMax and inspect/edit it.
-Use CryBlend or 3dsMax's CryEngine plugin to export your file to CryEngine.
I can't imagine snapping is worth all of that...
Best of luck,