Honestly I normally find it hard to believe just with appearance based on hairstyle because people can always change their hairstyle.
However since this theory was so into detail I did have a feeling of agreement to it.
There is one thing I thought of concerning the teeth (or eyes), has part of what is to do with the book Sai was drawing. Since looking at the book has a similarity to taking the identity of the people Sai has killed, Suigetsu gaining the teeth might have something to do with taking the identity as well. If I look at it in that aspect then it could be possible. There are still plotholes in my theory of coarse (such as Zabuza being Suigetsu's senior) but the connection I'll leave it up until later if there will be any.