That's just plain wrong... The third Raikage was known for his "Ultimate shield (being his incredibly tough skin), and his ultimate spear (His Chidori like attack)". It was never stated in the manga that the THIRD raikage was the fastest other than Minato..
Hell, even in the manga it's shown that the third Raikage only had a slightly above average speed. It was the FOURTH Raikage (A) that was the fastest behind Minato. And, considering Naruto NEEDED KM to be able to get past Raikage, and I believe it's safe to say that KM is substantially faster than SM, Naruto will need KM to avoid Ameterasu.
My point being: The fourth Raikage is faster than the third Raikage.
EDIT
Upon further investigation (and I'm not sure if Narutopedia can be called a reliable source), it would seem that it was stated that the Third Raikage's speed was On-par with his son's (A). So, I suppose (in theory, and if the information is correct about the third's speed) that Naruto MAY be able to dodge Ameterasu whilst in SM...
However: During the Fourth Raikage's battle with Sasuke, one of his bodyguards (can't remember the name) said that A was going to use a "teleportation" technique. Which is what made him able to avoid Ameterasu. So, I still doubt that naruto would be able to avoid Ameterasu with just SM.