I saw that there is now a Weatherwax collie kennel name granted by the AKC. Does this mean Lassie and all the line dogs are now AKC registered?

No, none of the line dogs have ever been, and are not now, AKC registered.

According the AKC, Bob Weatherwax applied for the kennel name of Weatherwax and asked for a special exception to the usual breeder criteria because his family had been breeding collies for over 50 years. He was granted an exception based on the family's public record and all this does is reserve the name Weatherwax to him, and only for the collie breed. He couldn't use it to register Cairn Terriers for example, he'd have to re-apply for the kennel name under that breed. Anyone else could apply for the use of the name Weatherwax for a kennel for any other breed other than collies. This granting of a kennel name does not in any way deem Lassie, Bob's collie, or any of the other living line dogs, as AKC registered dogs.