That fight looked like some circus act. SNV had 15'' height advantage over Dominguez (7'0'' vs 5'9''). Can't imagine there were bigger difference in height in any pro fight.
Cool question, wish the records were strong enough to get a real answer. Carnera would probably be the best shot at equaling it. He was way smaller than Valuev (he was kinda his era's equivalent to Valuev, though), but he fought a lot of bums that they probably don't have height info on. Think he was 6'6, so he'd have had to fight someone 5'3 to match that mark. Unlikely but possible.
Or Willard. Generally listed as 6'5" or 6'6" and fought in an earlier era with more short guys, but there's almost no info on some of those early opponents. Shortest listed height of an opponent that I see is 5'10 1/2 (Soldier Kearns). Regardless, probably doesn't beat the Valuev height advantage against anyone.