Tend to agree with the man from woodulike.
only problem with battening the floor is that the purpose of laying a DPM is to prevent the moisture in the concrete(which incidentally will take at least a year to dry out) from going into the wood.
If you fix the battens to the floor your going to...
Oak flooring is generally not too good for a bathroom area. If you really want to use it make sure its well sealed and a good expansion gap is left around the outside edge.
Generally an engineered board is more stable and the look should be exactly the same.