If we hand out "advantages" based on grappling pedigrees, then yes, Werdum had a significant one over Nog. However, this is MMA--not ADCC or the Mundials--and Nogueira managed to hang with Werdum on the ground.
Pedigree can indicate a lot, but honestly it's not a definitive way of looking at who will have the edge on the ground. Look at UFC 85 for instance:
Kevin Burns--a recent blue belt in BJJ--submitted Roan Carneiro--a world-class BJJ champion--with a triangle-choke. No one saw that coming, but it goes to show that MMA-BJJ and standard BJJ are not synonymous in the least.
So Nog could hang with Werdum in the ground even though Werdum has the better grappling pedigree, thanks. Pretty much confirms that MMA grappling!=Grappling.