Does the island in the middle of the lake connected by the Seventeen-Arch Bridge have a ferry pier?

Yes, you can go to the wharf at Xi Ti or under Wan Shou Mountain, there are boats.
The Seventeen-Arch Bridge in the Summer Palace connects the South Lake Island to the west and the Kuoruting to the east. It is the only land passage to the South Lake Island and does not have a ferry wharf.