Well I applied the fix, and I'm still not getting any hits.
I suppose it would be more accurate to say that foundIntersection is never true.
Code:
//Generate some plants. This method will be replaced by voxel plants later.
            int numTrees = rand() % 10;
            int numPlants = rand() % 15;
            Ogre::Vector4 * plantList = new Ogre::Vector4[numTrees + numPlants];
            PolyVox::RaycastResult groundCheckResult;
            Raycast<LargeVolume, MaterialDensityPair44> groundCheck(mWorldVoxels, Vector3DFloat(0,0,0), Vector3DFloat(0,0,0), groundCheckResult);
            for(int i = 0; i < numTrees; i++)
            {
               int x = rand() % 32 + 1;
               int z = rand() % 32 + 1;
               x += reg.getLowerCorner().getX();
               z += reg.getLowerCorner().getZ();
               stringstream test;
               test << "Chunk Number: " << x / 32 << " " << reg.getLowerCorner().getY() / 32 << " " << z / 32 << "\n"; 
               test << "generated coordinates: " << x << " " << z << "\n";
               OutputDebugString(test.str().c_str());
               groundCheck.setStart(Vector3DFloat(x,75,z));
               groundCheck.setDirection(Vector3DFloat(0,-1,0));
               groundCheck.execute();
               //If we hit something
               if(groundCheckResult.foundIntersection)
               {
                  OutputDebugString("Hit!\n");
                  //check if it is within bounds
                  if(groundCheckResult.intersectionVoxel.getY() < reg.getUpperCorner().getY() && groundCheckResult.intersectionVoxel.getY() > 32 && groundCheckResult.intersectionVoxel.getY() > -64)
                  {
                     plantList[i] = Ogre::Vector4(x,groundCheckResult.intersectionVoxel.getY(),z,0);
                     stringstream ss;
                     ss << "new loc" << plantList[i].x << " " << plantList[i].y << " " << plantList[i].z << " " << plantList[i].w << "\n";
                     OutputDebugString(ss.str().c_str());
                  }
                  else
                     break;
               }
            }
I never get the "Hit!" debug message which would indicate that my ray never hits anything in my volume.
I am now using a proper direction, but it still never hits anything in my volume. I'm following the example pretty closely, I'm not sure where I could be going wrong this time.