I'm a bit confused, I've never heard of a rule where you could not jump with a leather tip. Where did you hear that?
Now if you are talking about using JUST your shaft to jump, that is not legal, it needs to be a cue not just your shaft.
All those cues need to be buried in a landfill anyway, they make people think they are good at something when they are not and allow shots that should not be doable on a pool table. The WPA is probably just afraid to lose sponsor money if they ban jump cues, I have yet to hear a pro say they'd want jump cues in the rules, the all say they use them because others do. If given the option, they would have no jump cues.