jsPlumb doesn't have a Gantt chart connector out of the box, but someone wrote one a year or two ago:
http://help-me-hackers.com/tasks/107
which, when i saw it, i thought was pretty cool. I don't know a great deal about it, since it's all in Japanese, but the idea of polishing those connectors up and then adding them to jsPlumb for everyone to use is quite appealing.
i think perhaps the code is in this github project:
https://github.com/komagata/jquery.ganttView
..but be aware if you do try to integrate them, the code has moved on a little since they were written so you might have a little bit of work to do up front. I'd be happy to help you if you want to pursue this.
