The dump folder actually contains debug info, generated by the client when it crash. If you delete the silkerrsender, the dump files are generated but not sent to the server. Is not really necessary delete the folder, with the silkerrsender is enough.
With the dmp files Joymax can know what was you doing since you started the client until it crashed, and they can also view programs which were interacting with the client. For example my dump files contains info about xfire, because the xfire in-game mode interacts with the client.