It may not be quite the same. I would expect PAP, tilt, and rotation to be different for a lefty than a backup righty. But, assuming a righty can create a fairly normal lefty-looking release throwing backup, then you're probably going to see a very muted reaction.
Think about it for a second. A lefty's track is going to be on the other side of the finger holes, and for many normal drillings, that's going to result in the pin being in or near the track. Equivalent to a very long pin-PAP distance. I'd expect negative side weight and the reaction characteristics that would have. If, for some reason, a righty's grip fit a lefty's hand perfectly (which it probably won't), the lefty probably would get a much tamer reaction out of it.
I'd expect a backup bowler to be a little different, since there's no telling what happens to the PAP when you rotate your hand the other way around the ball.
SH
