If you have them on hand, then testing the two would answer the question authoritatively for you ... I always prefer to measure things for myself or experiment for myself when I can rather than take someone else's word for something .
The SG of water is 1.000. If sugar is dissolved in the water, the SG will be greater than 1.0, and how far above 1.0 depends on the ratio of water:sugar. Water with alcohol and no sugar will have a SG < 1.0 and how far below 1.0 depends on the ratio of water:alcohol.
Just thinking of that principle, you can see that by changing the amount of residual sugar, or amount of alcohol will change the SG. If a sweetness number is derived by the amount of unfermented sugar is in the wine, then it would follow that two wines with the same sweetness number, but different alcohol levels will have different SG. I would think that a sweetness number probably indicates a range rather than a consistent amount, though, so some variation would be likely eve with the same numbers.