so as to increase awareness of posture, yes it could eventually help tennis but placing a pipe against spine does basically nothing in correcting posture. in fact it could as well have negative effect.
posture is an extremely complex subject. one basic nature of it is the relaxed state posture and doing something posture are very different. but the relaxed state posture has huge implication for the dynamic posture. the pipe thing applies more to the relaxing posture but still not for everyone. dynamic posture cannot be approached by appearance or externally. I don't think the method that helpful for posture.