[Morsul the Dark]

Not quite knowledgable however

Gandalf sqays this "They barely even know of the existence of hobbits for which I am very thankful."

Also Sauron most likely only watched out for great doings and those that would make trouble for him since hobbits did very little in the way of great deeds he most likely be unfamiliar with such a place.

Also Sauron may have bin a bit of a shock seeing how far his ring had actually traveled thinking it to be in the hands of a man or an elf