I'm not quite sure what you mean, but my tool Jetstrap (http://jetstrap.com/) has grid support. You can drag in a grid row and then drag in grid columns. The UX on the grids isn't quite where I want it yet though.
a WYSIWYG editor may not suitable for layout manager. The idea is separating content from the template (layout/grid). However Bootstrap Live Editor also provides a basic grid insertion function as in the demo, which can be used to insert multi column text, etc.