Yes gravity, and to a lesser extent rotation, have a (somewhat unintuitive) impact on how the sea level will change across different parts of the globe. There's a good overview of this topic here: https://www.theguardian.com/environment/ng-interactive/2018/...
The sea level as it stands today is already effected by gravity. And this is in fact built into the wgs84 datum. So vertical elevation is measured relative to that assumed sea level after the effects of gravity. And a rise in sea level would presumably be measured relative to that existing datum.
