You've got to be kidding me. After six years in the Presidency and winning election twice, don't you think that the democrat attack machine wouldn't have fully researched this? I'll bet James Carville personally has dosiers on every Bush employee going back decades.
I don't know if you've lived in Texas, but I lived in El Paso during the Carter administration when immigration laws were enforced--lots of nice Anglo ladies had full-time maids and nannies and yardmen. They ignored the law until their cars got impounded for transporting illegals.
Not many patricians and aristocrats resisted the temptation to be waited on and cleaned up after by cheap and humble help. And I certainly don't recall any claim by the Bushes that they "never" did such a thing--
And if such a fact came to light, it'd put the seal of doom on any amnesty effort.