As my previous speakers already told you, the current ur_diver only support the follow_joint_trajectory interface (http://docs.ros.org/api/control_msgs/html/action/FollowJointTrajectory.html
Streaming positions or velocities is currently (not yet) supported...I've been playing around to enable ros-control concepts to be used with the UR, but haven't come far yet due to lack of time.
However, if you'd like to only get joint_states from your UR and not use the driver for programming, you could also use this test script
that I wrote once..
.it listenst to the RT port and publishes joint_states...