Depends what you consider dominating. I personally think at best he would top out around the same amount of points today's best do, and that's if he grew up and trained in this era. Gretzky in the 80s was 6 feet tall and 165 pounds, physically weak and not overly fast compared to the elite smaller guys today. There is no way a guy with the physical stature, strength, and lack of speed he had could dominate the way the game is played today. Also though, the game today is very lopsided towards the physical aspect and hockey sense doesn't shine as much as it once did, which is a shame. I think it may be headed in a better direction.
Who cares?
The measure of greatness is transcendence. Benefiting from technological advantages and being a byproduct of the evolution of a sport or thing aren't things that make someone greater than one who was more transcendent during his own time.
Is Bill Nye the Sciene Guy a "greater" intellectual than someone like Plato? He probably knows more about the natural world and whatnot, but that's because science has advanced so much since ancient times and he's been able to absorb knowledge that has been discovered. If it hadn't been for thinkers like Plato and Socrates, though, we might not be where we are now scientifically.
Similarly, Gretzky had no technological advantages during his own than anyone else and he simply dominated in a way players today don't relative to their peers. Therefore, he is to be considered greater than any current player.
You can say guys are faster, they skate better, they train harder etc, but if it hadn't been for previous generations, the sport wouldn't be at the point it's at now.
Gretzky may or not be as dominant as if he was playing now, but if it hadn't been for the driving forward of the evolution of hockey that he and other previous greats caused, modern players wouldn't be what they are now.
Therefore, if you eliminate him and other 80s and pre-80s greats from the equation, we don't get to the point we're at now to begin with.
You don't give someone more credit than someone from an older generation because of the extent to which they benefit indirectly from evolution.