The only wreck around the Sosua area that's divable is the Zinguara, a 100 foot bananna cargo ship that was sunk on purpose about 15 years ago for the divers. There are other wrecks around, but they are too deep for diving. There are Spanish Gallions around Monti Christi, but they are very deteriorated and in a marine preserve and not divable. There may be some wrecks around Monti Christi and Punta Rusia, but you'll have to check with the locals there as I don't have any information on them.
As far as caves go, there are thousands of caves on this island, most haven't been explored, and most require cave certification and cave diving equipment. There is a cavern dive at Lake Du Du which is east of Cabrera which is a very nice dive.