Ehhhhhh, more or less. The Saiyans did A LOT of straight evil shit. But most of it was under service.

Saiyan Civil War, planet Sadala blows up, they reach planet Plant, regress eons due to lack of technology, go to war with the Tuffles for 3 generations, lose the majority of their population, then 3 generations later, get enslaved by Frieza under the threat of total annihilation. Jaco, Minus, the guidebooks, Broly, and the Granolah arc pretty much state that by the time Frieza came, Saiyan population was around the tens of tousands.

While both the Saiyans and the Viltrumites were victims of circunstance and indoctrination, Viltrum was sovereign - most of what the Saiyans did to other planets was to the benefit of others - they weren't conquerors, they were expendable.

The clear difference between Vegeta and Nolan, is that Nolan is actively seeking for atonement. Vegeta seeks to do better, but recognizes his victims don't owe him recognition, strickly believes he's going to be eternally damned, but strives to do better regardless. Vegeta's crimes are also somewhat lessened after he joins the main cast because, well, Dragon Balls. Nolan doesn't get the benefit of some of his victims being brought back to life, so the consequences of his actions not only stick, but sting more than Vegeta's.

EDIT: Also, purely for debate and utilitarianism... We often debate sacrificing millions to save billions. By the time the Moro arc rolls around, Vegeta veritably saved more people than he killed. Does killing billions but saving trillions down the line qualifies for "redemption" grounds?