Does this mean that creating dirt for gus is now possible?
Yes.
You can see that if you play a LX mod with a Gusanos map (most LX mods use dirt here and there).
For Gusanos, there is no way at the moment to use that. Any suggestion about how you would like to use it? I guess the easiest way is to add an action which places the dirt. In LX, I think there are 5 predefined sized dirt balls (sized 1 to 5 pixels). It should be easy to just map those to Gus actions. But I can also give some more low level access if that could be interesting. For example, I could add some way to just change the material index to whatever.