For more information on simulating Grizzly, see grizzly_simulator.
To view the Grizzly model and TF transform tree in isolation, disconnected from a real or simulated robot, use the following launcher:
roslaunch grizzly_viz view_model.launch
You can change joint positions using joint state publisher gui:
To visualize a real or simulated Grizzly, launch:
roslaunch grizzly_viz view_robot.launch
You can click the Interact button in rviz, and use the interactive markers to give Grizzly some motion commands: