Yea this is an old bug that is somehow still apparent.
A functional (yet annoying) workaround is (before you open hammer) change the AppID, found in the gameinfo.cfg, from 440 to 218 (i think, someone please correct my AppID numbers if im wrong). This will allow you to see wireframes in Hammer. Now when you load GES it may crash or not load, if this happens you need to change the AppID back to 440 before launch. Disable auto-launch after compile in Hammer to make this slightly less painful.