Hi,
I'm not an epert on these ships, but Staff's book on German battlecruisers has an image of Derfflinger entering Wilhelmshaven after the battle and the funnel of a steamboat can be seen amidships. It can also be seen here in this image of Derfflinger in harbour after the battle, along with a rowing boat next to it.
Assuming the images are correctly labelled, it would show the boats on board.