On the Grid
If you've ever discussed the idea of designing levels for the Source Engine in 3ds Max, the odds are that the topic of the grid has come up. In Source, keeping world geometry vertices aligned to the world grid is very important to successfully compile levels into Source becuse of how the BSP compilers work. World geometry that is not aligned to the grid is prone to create either leaks or microbrushes--both of which are bad.
A long history of Source Engine workflows have turned into community wisdom on this topic that, in reality, is not entirely accurate. Traditionally, all level design was in Hammer and all the models were in external "modeling" applications. Because models, built in these external applications (like 3ds Max, Maya, Blender, Milkshape 3D, etc), do not have to keep all vertices aligned to the grid, a common misconception has developed in the Source Engine world that the external applications are incapable of being used to do Source Engine level design; the Source Engine community has confused the tradition of Source Engine development as a technical reason for not using external applications.
In terms of 3ds Max, which is what the Wall Worm pipeline uses, the only real hurdle is for level designers to first let go of the preconceptions about the grid in 3ds Max and then to become familiar with the tools in Max. Just because you can make objects like models that don't worry about the grid, it does not mean that Max's grid tools are inherently different than those in Hammer. You can build geometry in 3ds Max just as easily (or even more easily as you learn more tools) as Hammer.
Success in building worlds in 3ds Max starts with aligning the World Units in Max to those in Source. This means that your Units should be set to Generic Units where each unit equals one inch. You can set that via the Customize > Customize Units dialog.
Next, you should become familiar with the different snap modes, including 2D, 2.5D and 3D snaps. The best way to understand them is to watch the Autodesk video on snaps (embedded below). The main thing to keep in mind is that 2D and 2.5D snaps should only be using in orthographic views (Top, Left, Front, etc) and the 3D snap should only be used in the Perspective view.
Finally, for basic level design (and world geometry blocking) you should limit the active snaps to Snap to Grid and/or Snap to Vertex. This will save you a lot of time.
You should read the documentation on snaps in 3ds Max as it relates to snap overrides and all the various snap settings.
In the end, there is no fundamental difference between the grid in Hammer and that in 3ds Max.
Also, several geometry objects made by Wall Worm specifically for BSP game design have a parameter to turn on grid snapping. These geometry objects will have all vertices snapped to the grid automatically when this option is turned on. The geometry with these controls are CorVex, ShellVex and Arch.