Without turning this into a biomechanical debate, Tim is correct in that the further away the bar is from the body, the higher torque on the spine. here is a picture I just did up quickly to to illustrate this.
But anyways, a T-bar row would have to be easier on the spine, compared to a bent over row, since the bar is closer to the body. Having said all this, i think there's an argument to be made that any ergonomist/biomechanist would agree that doing exercises such as deadlifting 500 lbs for example, are not good for your back. Sure, you can use proper form on them, but either way, it's going to create a lot of force on the spine, that's just the nature of the lift.
But it's so easy to get carried away with this argument for weight lifters. For one, the body does adapt to accommodate to the stressor, but two, we know that these exercises create force, but oh well, we want to be able to deadlift 500 lbs because it's a great way to build muscle and because it's cool to do.
My advice, just do exercises correctly with good form, try and keep a neutral spin.
Edit: I picked those values for the calculations for simplicity sake. Thus, those who seem to search the forum high and low looking for things to nitpick *cough Duality cough* please don't point out that holding a bar 2 meters away from the body in your arms is not possible. Doubling the torque still applies if we hold the bar 0.1 meters away, and 0.2 meters away.