Greenland rebounding does absolutely nothing because the "extra" volume is not taken out of the ocean. The water doesn't suddenly jump back up on the land.
It is true that Greenland rebounding won't affect sea level, but not for the reason parent seems to imply. The real reason is that when a land mass is pressed downwards by an ice sheet, it sinks because it displaces material in the mantle. That mantle material is squeezed out sideways, and ends up raising adjacent land masses or ocean floor.
When the ice sheet melts, the displaced mantle flows back, the depressed land rebounds, and the raised adjacent land or ocean floor sinks back.
This effect is currently causing the Netherlands to sink at a rate of about five millimeters per year, while Scandinavia is rising at a similar rate. The rebound from the last glacial, in other words, is still ongoing, and quite significant. (Having to raise sea dikes by half a meter over a century, even without global warming induced sea level rise, is a pain in the ass and not something you can just ignore...)
If Greenland losing its ice and rising causes no dry land to sink but only ocean floor, that floor sinkage will compensate for some of the sea level rise, but not quickly enough to help us save our coastal lands and cities.