No.

Absolute neutral buoyancy can only be obtained theoretically. Submarines can only maintain their depth for long periods by maintaining headway and using the planes and altering the trim.

A derelict submarine would not be able to maintain level trim and once trim is lost, it tends to not be self correcting but will get worse and equipment/fluids flow/fall to the lower end, pushing it further down and the other end up. A derelict Submarine, if positively bouoyant would be found in a more vertical attitude (bow up or bow down).

A derelict submarine would either end up at the surface or at the bottom. Any variation of salinity of the ocean would cause the buoyancy to change. Sea temperature will have the same effect. One could imagine the decomposing 50+ people would also have some effect.

But in any case, a derelict submarine could not maintain a steady depth for very long.

Now, a derelict submarine may bob just at the surface. It would not surface as in a deliberate surfaced submarine (hull and superstructure out of the water), but it would be just at the surface with most of the hull below the surface and only the superstructure and the bow/stern out of the water.