You could be right, I was just lumping them together as 'not covered anywhere else'. One further connection is that Ferry moves along the River, but it could be regarded as a multi-cell non-capturer moving along a pair of ranks. They seem to me to fall into three groups.
The Ferry, Halter, and Trampoline can all move, either under their own steam or with the aid of another piece, but cannot capture and have a different effect on pieces. They can therefore be considered special cases of non-capturing pieces.
The Raft and Tardis are board sections that move - and again do not capture. They take their pieces with them.
The Bridge, Fortress, and River do not change their location on the board but still affect how pieces move.