I read an article where a collie judge said that Lassie couldn't be an AKC dog because of the white on her face. Is that true?

No, that is absolutely false.

The AKC doesn't really care what a dog looks like. They register dogs based on registration papers. If the mother and father are registered with the AKC as collies, the pups are automatically assumed to be collies (another reason to buy your collie from a reputable breeder and not a pet shop). The AKC keeps "standards" of what the ideal collie should look like and those are formed in partnership with the Collie Club of America. White on the face is allowed and common in certain collie lines.

In the purebred world of show dogs, collies are judged based on the dog that comes closest to the "standard". Anything that deviates from that standard is called a "fault". The white blaze is not a fault.