Answer
Yes, this would still hold true.
Work Step by Step
The equation $Q = cm \Delta T$ relates the heat transferred in or out, to the body's temperature change. The hot rock will cool down and the water will warm up, regardless of the relative amounts of each.
The rock loses as much internal energy as the water gains. However, the overall change in the ocean’s temperature would be too small to measure because "m" is so large.