The LCDD geometry needs to be dumped to plain GDML to be loaded by ROOT.
You can use a script similar to the following to load a plain GDML file into ROOT.
void gdmlTest()
{
char* testfile="./test.gdml";
gSystem->Load("libGeom");
gSystem->Load("libGdml");
TGeoManager::Import(testfile);
gGeoManager->GetTopVolume()->Draw("ogl");
}
This command should display the ROOT OpenGL viewer with the geometry from the test.gdml file.